database package

Firebase Realtime Database

Functions

Function	Description
function(app, ...)
getDatabase(app, url)	Returns the instance of the Realtime Database SDK that is associated with the providedFirebaseApp. Initializes a new instance with default settings if no instance exists or if the existing instance uses a custom database URL.
function(db, ...)
connectDatabaseEmulator(db, host, port, options)	Modify the provided instance to communicate with the Realtime Database emulator. Note: This method must be called before performing any other operation.
goOffline(db)	Disconnects from the server (all Database operations will be completed offline).The client automatically maintains a persistent connection to the Database server, which will remain active indefinitely and reconnect when disconnected. However, the`goOffline()` and`goOnline()` methods may be used to control the client connection in cases where a persistent connection is undesirable.While offline, the client will no longer receive data updates from the Database. However, all Database operations performed locally will continue to immediately fire events, allowing your application to continue behaving normally. Additionally, each operation performed locally will automatically be queued and retried upon reconnection to the Database server.To reconnect to the Database and begin receiving remote events, see`goOnline()`.
goOnline(db)	Reconnects to the server and synchronizes the offline Database state with the server state.This method should be used after disabling the active connection with`goOffline()`. Once reconnected, the client will transmit the proper data and fire the appropriate events so that your client "catches up" automatically.
ref(db, path)	Returns a`Reference` representing the location in the Database corresponding to the provided path. If no path is provided, the`Reference` will point to the root of the Database.
refFromURL(db, url)	Returns a`Reference` representing the location in the Database corresponding to the provided Firebase URL.An exception is thrown if the URL is not a valid Firebase Database URL or it has a different domain than the current`Database` instance.Note that all query parameters (`orderBy`,`limitToLast`, etc.) are ignored and are not applied to the returned`Reference`.
function()
forceLongPolling()	Force the use of longPolling instead of websockets. This will be ignored if websocket protocol is used in databaseURL.
forceWebSockets()	Force the use of websockets instead of longPolling.
orderByKey()	Creates a new`QueryConstraint` that orders by the key.Sorts the results of a query by their (ascending) key values.You can read more about`orderByKey()` inSort data.
orderByPriority()	Creates a new`QueryConstraint` that orders by priority.Applications need not use priority but can order collections by ordinary properties (seeSort data for alternatives to priority.
orderByValue()	Creates a new`QueryConstraint` that orders by value.If the children of a query are all scalar values (string, number, or boolean), you can order the results by their (ascending) values.You can read more about`orderByValue()` inSort data.
serverTimestamp()	Returns a placeholder value for auto-populating the current timestamp (time since the Unix epoch, in milliseconds) as determined by the Firebase servers.
function(delta, ...)
increment(delta)	Returns a placeholder value that can be used to atomically increment the current database value by the provided delta.
function(enabled, ...)
enableLogging(enabled, persistent)	Logs debugging information to the console.
function(limit, ...)
limitToFirst(limit)	Creates a new`QueryConstraint` that if limited to the first specific number of children.The`limitToFirst()` method is used to set a maximum number of children to be synced for a given callback. If we set a limit of 100, we will initially only receive up to 100`child_added` events. If we have fewer than 100 messages stored in our Database, a`child_added` event will fire for each message. However, if we have over 100 messages, we will only receive a`child_added` event for the first 100 ordered messages. As items change, we will receive`child_removed` events for each item that drops out of the active list so that the total number stays at 100.You can read more about`limitToFirst()` inFiltering data.
limitToLast(limit)	Creates a new`QueryConstraint` that is limited to return only the last specified number of children.The`limitToLast()` method is used to set a maximum number of children to be synced for a given callback. If we set a limit of 100, we will initially only receive up to 100`child_added` events. If we have fewer than 100 messages stored in our Database, a`child_added` event will fire for each message. However, if we have over 100 messages, we will only receive a`child_added` event for the last 100 ordered messages. As items change, we will receive`child_removed` events for each item that drops out of the active list so that the total number stays at 100.You can read more about`limitToLast()` inFiltering data.
function(logger, ...)
enableLogging(logger)	Logs debugging information to the console.
function(parent, ...)
child(parent, path)	Gets a`Reference` for the location at the specified relative path.The relative path can either be a simple child name (for example, "ada") or a deeper slash-separated path (for example, "ada/name/first").
push(parent, value)	Generates a new child location using a unique key and returns its`Reference`.This is the most common pattern for adding data to a collection of items.If you provide a value to`push()`, the value is written to the generated location. If you don't pass a value, nothing is written to the database and the child remains empty (but you can use the`Reference` elsewhere).The unique keys generated by`push()` are ordered by the current time, so the resulting list of items is chronologically sorted. The keys are also designed to be unguessable (they contain 72 random bits of entropy).SeeAppend to a list of data. SeeThe 2^120 Ways to Ensure Unique Identifiers.
function(path, ...)
orderByChild(path)	Creates a new`QueryConstraint` that orders by the specified child key.Queries can only order by one key at a time. Calling`orderByChild()` multiple times on the same query is an error.Firebase queries allow you to order your data by any child key on the fly. However, if you know in advance what your indexes will be, you can define them via the .indexOn rule in your Security Rules for better performance. See thehttps://firebase.google.com/docs/database/security/indexing-data rule for more information.You can read more about`orderByChild()` inSort data.
function(query, ...)
get(query)	Gets the most up-to-date result for this query.
off(query, eventType, callback)	Detaches a callback previously attached with the corresponding`on()` (`onValue`,`onChildAdded`) listener. Note: This is not the recommended way to remove a listener. Instead, please use the returned callback function from the respective`on` callbacks.Detach a callback previously attached with`on*()`. Calling`off()` on a parent listener will not automatically remove listeners registered on child nodes,`off()` must also be called on any child listeners to remove the callback.If a callback is not specified, all callbacks for the specified eventType will be removed. Similarly, if no eventType is specified, all callbacks for the`Reference` will be removed.Individual listeners can also be removed by invoking their unsubscribe callbacks.
onChildAdded(query, callback, cancelCallback)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildAdded` event will be triggered once for each initial child at this location, and it will be triggered again every time a new child is added. The`DataSnapshot` passed into the callback will reflect the data for the relevant child. For ordering purposes, it is passed a second argument which is a string containing the key of the previous sibling child by sort order, or`null` if it is the first child.
onChildAdded(query, callback, options)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildAdded` event will be triggered once for each initial child at this location, and it will be triggered again every time a new child is added. The`DataSnapshot` passed into the callback will reflect the data for the relevant child. For ordering purposes, it is passed a second argument which is a string containing the key of the previous sibling child by sort order, or`null` if it is the first child.
onChildAdded(query, callback, cancelCallback, options)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildAdded` event will be triggered once for each initial child at this location, and it will be triggered again every time a new child is added. The`DataSnapshot` passed into the callback will reflect the data for the relevant child. For ordering purposes, it is passed a second argument which is a string containing the key of the previous sibling child by sort order, or`null` if it is the first child.
onChildChanged(query, callback, cancelCallback)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildChanged` event will be triggered when the data stored in a child (or any of its descendants) changes. Note that a single`child_changed` event may represent multiple changes to the child. The`DataSnapshot` passed to the callback will contain the new child contents. For ordering purposes, the callback is also passed a second argument which is a string containing the key of the previous sibling child by sort order, or`null` if it is the first child.
onChildChanged(query, callback, options)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildChanged` event will be triggered when the data stored in a child (or any of its descendants) changes. Note that a single`child_changed` event may represent multiple changes to the child. The`DataSnapshot` passed to the callback will contain the new child contents. For ordering purposes, the callback is also passed a second argument which is a string containing the key of the previous sibling child by sort order, or`null` if it is the first child.
onChildChanged(query, callback, cancelCallback, options)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildChanged` event will be triggered when the data stored in a child (or any of its descendants) changes. Note that a single`child_changed` event may represent multiple changes to the child. The`DataSnapshot` passed to the callback will contain the new child contents. For ordering purposes, the callback is also passed a second argument which is a string containing the key of the previous sibling child by sort order, or`null` if it is the first child.
onChildMoved(query, callback, cancelCallback)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildMoved` event will be triggered when a child's sort order changes such that its position relative to its siblings changes. The`DataSnapshot` passed to the callback will be for the data of the child that has moved. It is also passed a second argument which is a string containing the key of the previous sibling child by sort order, or`null` if it is the first child.
onChildMoved(query, callback, options)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildMoved` event will be triggered when a child's sort order changes such that its position relative to its siblings changes. The`DataSnapshot` passed to the callback will be for the data of the child that has moved. It is also passed a second argument which is a string containing the key of the previous sibling child by sort order, or`null` if it is the first child.
onChildMoved(query, callback, cancelCallback, options)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildMoved` event will be triggered when a child's sort order changes such that its position relative to its siblings changes. The`DataSnapshot` passed to the callback will be for the data of the child that has moved. It is also passed a second argument which is a string containing the key of the previous sibling child by sort order, or`null` if it is the first child.
onChildRemoved(query, callback, cancelCallback)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildRemoved` event will be triggered once every time a child is removed. The`DataSnapshot` passed into the callback will be the old data for the child that was removed. A child will get removed when either:- a client explicitly calls`remove()` on that child or one of its ancestors - a client calls`set(null)` on that child or one of its ancestors - that child has all of its children removed - there is a query in effect which now filters out the child (because it's sort order changed or the max limit was hit)
onChildRemoved(query, callback, options)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildRemoved` event will be triggered once every time a child is removed. The`DataSnapshot` passed into the callback will be the old data for the child that was removed. A child will get removed when either:- a client explicitly calls`remove()` on that child or one of its ancestors - a client calls`set(null)` on that child or one of its ancestors - that child has all of its children removed - there is a query in effect which now filters out the child (because it's sort order changed or the max limit was hit)
onChildRemoved(query, callback, cancelCallback, options)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onChildRemoved` event will be triggered once every time a child is removed. The`DataSnapshot` passed into the callback will be the old data for the child that was removed. A child will get removed when either:- a client explicitly calls`remove()` on that child or one of its ancestors - a client calls`set(null)` on that child or one of its ancestors - that child has all of its children removed - there is a query in effect which now filters out the child (because it's sort order changed or the max limit was hit)
onValue(query, callback, cancelCallback)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onValue` event will trigger once with the initial data stored at this location, and then trigger again each time the data changes. The`DataSnapshot` passed to the callback will be for the location at which`on()` was called. It won't trigger until the entire contents has been synchronized. If the location has no data, it will be triggered with an empty`DataSnapshot` (`val()` will return`null`).
onValue(query, callback, options)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onValue` event will trigger once with the initial data stored at this location, and then trigger again each time the data changes. The`DataSnapshot` passed to the callback will be for the location at which`on()` was called. It won't trigger until the entire contents has been synchronized. If the location has no data, it will be triggered with an empty`DataSnapshot` (`val()` will return`null`).
onValue(query, callback, cancelCallback, options)	Listens for data changes at a particular location.This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.An`onValue` event will trigger once with the initial data stored at this location, and then trigger again each time the data changes. The`DataSnapshot` passed to the callback will be for the location at which`on()` was called. It won't trigger until the entire contents has been synchronized. If the location has no data, it will be triggered with an empty`DataSnapshot` (`val()` will return`null`).
query(query, queryConstraints)	Creates a new immutable instance of`Query` that is extended to also include additional query constraints.
function(ref, ...)
onDisconnect(ref)	Returns an`OnDisconnect` object - seeEnabling Offline Capabilities in JavaScript for more information on how to use it.
remove(ref)	Removes the data at this Database location.Any data at child locations will also be deleted.The effect of the remove will be visible immediately and the corresponding event 'value' will be triggered. Synchronization of the remove to the Firebase servers will also be started, and the returned Promise will resolve when complete. If provided, the onComplete callback will be called asynchronously after synchronization has finished.
runTransaction(ref, transactionUpdate, options)	Atomically modifies the data at this location.Atomically modify the data at this location. Unlike a normal`set()`, which just overwrites the data regardless of its previous value,`runTransaction()` is used to modify the existing value to a new value, ensuring there are no conflicts with other clients writing to the same location at the same time.To accomplish this, you pass`runTransaction()` an update function which is used to transform the current value into a new value. If another client writes to the location before your new value is successfully written, your update function will be called again with the new current value, and the write will be retried. This will happen repeatedly until your write succeeds without conflict or you abort the transaction by not returning a value from your update function.Note: Modifying data with`set()` will cancel any pending transactions at that location, so extreme care should be taken if mixing`set()` and`runTransaction()` to update the same data.Note: When using transactions with Security and Firebase Rules in place, be aware that a client needs`.read` access in addition to`.write` access in order to perform a transaction. This is because the client-side nature of transactions requires the client to read the data in order to transactionally update it.
set(ref, value)	Writes data to this Database location.This will overwrite any data at this location and all child locations.The effect of the write will be visible immediately, and the corresponding events ("value", "child_added", etc.) will be triggered. Synchronization of the data to the Firebase servers will also be started, and the returned Promise will resolve when complete. If provided, the`onComplete` callback will be called asynchronously after synchronization has finished.Passing`null` for the new value is equivalent to calling`remove()`; namely, all data at this location and all child locations will be deleted.`set()` will remove any priority stored at this location, so if priority is meant to be preserved, you need to use`setWithPriority()` instead.Note that modifying data with`set()` will cancel any pending transactions at that location, so extreme care should be taken if mixing`set()` and`transaction()` to modify the same data.A single`set()` will generate a single "value" event at the location where the`set()` was performed.
setPriority(ref, priority)	Sets a priority for the data at this Database location.Applications need not use priority but can order collections by ordinary properties (seeSorting and filtering data ).
setWithPriority(ref, value, priority)	Writes data the Database location. Like`set()` but also specifies the priority for that data.Applications need not use priority but can order collections by ordinary properties (seeSorting and filtering data ).
update(ref, values)	Writes multiple values to the Database at once.The`values` argument contains multiple property-value pairs that will be written to the Database together. Each child property can either be a simple property (for example, "name") or a relative path (for example, "name/first") from the current location to the data to update.As opposed to the`set()` method,`update()` can be use to selectively update only the referenced properties at the current location (instead of replacing all the child properties at the current location).The effect of the write will be visible immediately, and the corresponding events ('value', 'child_added', etc.) will be triggered. Synchronization of the data to the Firebase servers will also be started, and the returned Promise will resolve when complete. If provided, the`onComplete` callback will be called asynchronously after synchronization has finished.A single`update()` will generate a single "value" event at the location where the`update()` was performed, regardless of how many children were modified.Note that modifying data with`update()` will cancel any pending transactions at that location, so extreme care should be taken if mixing`update()` and`transaction()` to modify the same data.Passing`null` to`update()` will remove the data at this location.SeeIntroducing multi-location updates and more.
function(value, ...)
endAt(value, key)	Creates a`QueryConstraint` with the specified ending point.Using`startAt()`,`startAfter()`,`endBefore()`,`endAt()` and`equalTo()` allows you to choose arbitrary starting and ending points for your queries.The ending point is inclusive, so children with exactly the specified value will be included in the query. The optional key argument can be used to further limit the range of the query. If it is specified, then children that have exactly the specified value must also have a key name less than or equal to the specified key.You can read more about`endAt()` inFiltering data.
endBefore(value, key)	Creates a`QueryConstraint` with the specified ending point (exclusive).Using`startAt()`,`startAfter()`,`endBefore()`,`endAt()` and`equalTo()` allows you to choose arbitrary starting and ending points for your queries.The ending point is exclusive. If only a value is provided, children with a value less than the specified value will be included in the query. If a key is specified, then children must have a value less than or equal to the specified value and a key name less than the specified key.
equalTo(value, key)	Creates a`QueryConstraint` that includes children that match the specified value.Using`startAt()`,`startAfter()`,`endBefore()`,`endAt()` and`equalTo()` allows you to choose arbitrary starting and ending points for your queries.The optional key argument can be used to further limit the range of the query. If it is specified, then children that have exactly the specified value must also have exactly the specified key as their key name. This can be used to filter result sets with many matches for the same value.You can read more about`equalTo()` inFiltering data.
startAfter(value, key)	Creates a`QueryConstraint` with the specified starting point (exclusive).Using`startAt()`,`startAfter()`,`endBefore()`,`endAt()` and`equalTo()` allows you to choose arbitrary starting and ending points for your queries.The starting point is exclusive. If only a value is provided, children with a value greater than the specified value will be included in the query. If a key is specified, then children must have a value greater than or equal to the specified value and a a key name greater than the specified key.
startAt(value, key)	Creates a`QueryConstraint` with the specified starting point.Using`startAt()`,`startAfter()`,`endBefore()`,`endAt()` and`equalTo()` allows you to choose arbitrary starting and ending points for your queries.The starting point is inclusive, so children with exactly the specified value will be included in the query. The optional key argument can be used to further limit the range of the query. If it is specified, then children that have exactly the specified value must also have a key name greater than or equal to the specified key.You can read more about`startAt()` inFiltering data.

Classes

Class	Description
Database	Class representing a Firebase Realtime Database.
DataSnapshot	A`DataSnapshot` contains data from a Database location.Any time you read data from the Database, you receive the data as a`DataSnapshot`. A`DataSnapshot` is passed to the event callbacks you attach with`on()` or`once()`. You can extract the contents of the snapshot as a JavaScript object by calling the`val()` method. Alternatively, you can traverse into the snapshot by calling`child()` to return child snapshots (which you could then call`val()` on).A`DataSnapshot` is an efficiently generated, immutable copy of the data at a Database location. It cannot be modified and will never change (to modify data, you always call the`set()` method on a`Reference` directly).
OnDisconnect	The`onDisconnect` class allows you to write or clear data when your client disconnects from the Database server. These updates occur whether your client disconnects cleanly or not, so you can rely on them to clean up data even if a connection is dropped or a client crashes.The`onDisconnect` class is most commonly used to manage presence in applications where it is useful to detect how many clients are connected and when other clients disconnect. SeeEnabling Offline Capabilities in JavaScript for more information.To avoid problems when a connection is dropped before the requests can be transferred to the Database server, these functions should be called before writing any data.Note that`onDisconnect` operations are only triggered once. If you want an operation to occur each time a disconnect occurs, you'll need to re-establish the`onDisconnect` operations each time you reconnect.
QueryConstraint	A`QueryConstraint` is used to narrow the set of documents returned by a Database query.`QueryConstraint`s are created by invokingendAt(),endBefore(),startAt(),startAfter(),limitToFirst(),limitToLast(),orderByChild(),orderByChild(),orderByKey() ,orderByPriority() ,orderByValue() orequalTo() and can then be passed toquery() to create a new query instance that also contains this`QueryConstraint`.
TransactionResult	A type for the resolve value ofrunTransaction().

Interfaces

Interface	Description
DatabaseReference	A`DatabaseReference` represents a specific location in your Database and can be used for reading or writing data to that Database location.You can reference the root or child location in your Database by calling`ref()` or`ref("child/path")`.Writing is done with the`set()` method and reading can be done with the`on*()` method. Seehttps://firebase.google.com/docs/database/web/read-and-write
IteratedDataSnapshot	Represents a child snapshot of a`Reference` that is being iterated over. The key will never be undefined.
ListenOptions	An options objects that can be used to customize a listener.
Query	A`Query` sorts and filters the data at a Database location so only a subset of the child data is included. This can be used to order a collection of data by some attribute (for example, height of dinosaurs) as well as to restrict a large list of items (for example, chat messages) down to a number suitable for synchronizing to the client. Queries are created by chaining together one or more of the filter methods defined here.Just as with a`DatabaseReference`, you can receive data from a`Query` by using the`on*()` methods. You will only receive events and`DataSnapshot`s for the subset of the data that matches your query.Seehttps://firebase.google.com/docs/database/web/lists-of-data#sorting_and_filtering_data for more information.
ThenableReference	A`Promise` that can also act as a`DatabaseReference` when returned bypush(). The reference is available immediately and the`Promise` resolves as the write to the backend completes.
TransactionOptions	An options object to configure transactions.

Type Aliases

Type Alias	Description
EventType	One of the following strings: "value", "child_added", "child_changed", "child_removed", or "child_moved."
QueryConstraintType	Describes the different query constraints available in this SDK.
Unsubscribe	A callback that can invoked to remove a listener.

function(app, ...)

getDatabase(app, url)

Returns the instance of the Realtime Database SDK that is associated with the providedFirebaseApp. Initializes a new instance with default settings if no instance exists or if the existing instance uses a custom database URL.

Signature:

exportdeclarefunctiongetDatabase(app?:FirebaseApp,url?:string):Database;

Parameters

Parameter	Type	Description
app	FirebaseApp	TheFirebaseApp instance that the returned Realtime Database instance is associated with.
url	string	The URL of the Realtime Database instance to connect to. If not provided, the SDK connects to the default instance of the Firebase App.

Returns:

Database

TheDatabase instance of the provided app.

function(db, ...)

connectDatabaseEmulator(db, host, port, options)

Modify the provided instance to communicate with the Realtime Database emulator.

Note: This method must be called before performing any other operation.

Signature:

exportdeclarefunctionconnectDatabaseEmulator(db:Database,host:string,port:number,options?:{mockUserToken?:EmulatorMockTokenOptions|string;}):void;

Parameters

Parameter	Type	Description
db	Database	The instance to modify.
host	string	The emulator host (ex: localhost)
port	number	The emulator port (ex: 8080)
options	{ mockUserToken?:EmulatorMockTokenOptions \| string; }

Returns:

void

goOffline(db)

Disconnects from the server (all Database operations will be completed offline).

The client automatically maintains a persistent connection to the Database server, which will remain active indefinitely and reconnect when disconnected. However, thegoOffline() andgoOnline() methods may be used to control the client connection in cases where a persistent connection is undesirable.

While offline, the client will no longer receive data updates from the Database. However, all Database operations performed locally will continue to immediately fire events, allowing your application to continue behaving normally. Additionally, each operation performed locally will automatically be queued and retried upon reconnection to the Database server.

To reconnect to the Database and begin receiving remote events, seegoOnline().

Signature:

exportdeclarefunctiongoOffline(db:Database):void;

Parameters

Parameter	Type	Description
db	Database	The instance to disconnect.

Returns:

void

goOnline(db)

Reconnects to the server and synchronizes the offline Database state with the server state.

This method should be used after disabling the active connection withgoOffline(). Once reconnected, the client will transmit the proper data and fire the appropriate events so that your client "catches up" automatically.

Signature:

exportdeclarefunctiongoOnline(db:Database):void;

Parameters

Parameter	Type	Description
db	Database	The instance to reconnect.

Returns:

void

ref(db, path)

Returns aReference representing the location in the Database corresponding to the provided path. If no path is provided, theReference will point to the root of the Database.

Signature:

exportdeclarefunctionref(db:Database,path?:string):DatabaseReference;

Parameters

Parameter	Type	Description
db	Database	The database instance to obtain a reference for.
path	string	Optional path representing the location the returned`Reference` will point. If not provided, the returned`Reference` will point to the root of the Database.

Returns:

DatabaseReference

If a path is provided, aReference pointing to the provided path. Otherwise, aReference pointing to the root of the Database.

refFromURL(db, url)

Returns aReference representing the location in the Database corresponding to the provided Firebase URL.

An exception is thrown if the URL is not a valid Firebase Database URL or it has a different domain than the currentDatabase instance.

Note that all query parameters (orderBy,limitToLast, etc.) are ignored and are not applied to the returnedReference.

Signature:

exportdeclarefunctionrefFromURL(db:Database,url:string):DatabaseReference;

Parameters

Parameter	Type	Description
db	Database	The database instance to obtain a reference for.
url	string	The Firebase URL at which the returned`Reference` will point.

Returns:

DatabaseReference

AReference pointing to the provided Firebase URL.

function()

forceLongPolling()

Force the use of longPolling instead of websockets. This will be ignored if websocket protocol is used in databaseURL.

Signature:

exportdeclarefunctionforceLongPolling():void;

Returns:

void

forceWebSockets()

Force the use of websockets instead of longPolling.

Signature:

exportdeclarefunctionforceWebSockets():void;

Returns:

void

orderByKey()

Creates a newQueryConstraint that orders by the key.

Sorts the results of a query by their (ascending) key values.

You can read more aboutorderByKey() inSort data.

Signature:

exportdeclarefunctionorderByKey():QueryConstraint;

Returns:

QueryConstraint

orderByPriority()

Creates a newQueryConstraint that orders by priority.

Applications need not use priority but can order collections by ordinary properties (seeSort data for alternatives to priority.

Signature:

exportdeclarefunctionorderByPriority():QueryConstraint;

Returns:

QueryConstraint

orderByValue()

Creates a newQueryConstraint that orders by value.

If the children of a query are all scalar values (string, number, or boolean), you can order the results by their (ascending) values.

You can read more aboutorderByValue() inSort data.

Signature:

exportdeclarefunctionorderByValue():QueryConstraint;

Returns:

QueryConstraint

serverTimestamp()

Returns a placeholder value for auto-populating the current timestamp (time since the Unix epoch, in milliseconds) as determined by the Firebase servers.

Signature:

exportdeclarefunctionserverTimestamp():object;

Returns:

object

function(delta, ...)

increment(delta)

Returns a placeholder value that can be used to atomically increment the current database value by the provided delta.

Signature:

exportdeclarefunctionincrement(delta:number):object;

Parameters

Parameter	Type	Description
delta	number	the amount to modify the current value atomically.

Returns:

object

A placeholder value for modifying data atomically server-side.

function(enabled, ...)

enableLogging(enabled, persistent)

Logs debugging information to the console.

Signature:

exportdeclarefunctionenableLogging(enabled:boolean,persistent?:boolean):any;

Parameters

Parameter	Type	Description
enabled	boolean	Enables logging if`true`, disables logging if`false`.
persistent	boolean	Remembers the logging state between page refreshes if`true`.

Returns:

any

function(limit, ...)

limitToFirst(limit)

Creates a newQueryConstraint that if limited to the first specific number of children.

ThelimitToFirst() method is used to set a maximum number of children to be synced for a given callback. If we set a limit of 100, we will initially only receive up to 100child_added events. If we have fewer than 100 messages stored in our Database, achild_added event will fire for each message. However, if we have over 100 messages, we will only receive achild_added event for the first 100 ordered messages. As items change, we will receivechild_removed events for each item that drops out of the active list so that the total number stays at 100.

You can read more aboutlimitToFirst() inFiltering data.

Signature:

exportdeclarefunctionlimitToFirst(limit:number):QueryConstraint;

Parameters

Parameter	Type	Description
limit	number	The maximum number of nodes to include in this query.

Returns:

QueryConstraint

limitToLast(limit)

Creates a newQueryConstraint that is limited to return only the last specified number of children.

ThelimitToLast() method is used to set a maximum number of children to be synced for a given callback. If we set a limit of 100, we will initially only receive up to 100child_added events. If we have fewer than 100 messages stored in our Database, achild_added event will fire for each message. However, if we have over 100 messages, we will only receive achild_added event for the last 100 ordered messages. As items change, we will receivechild_removed events for each item that drops out of the active list so that the total number stays at 100.

You can read more aboutlimitToLast() inFiltering data.

Signature:

exportdeclarefunctionlimitToLast(limit:number):QueryConstraint;

Parameters

Parameter	Type	Description
limit	number	The maximum number of nodes to include in this query.

Returns:

QueryConstraint

function(logger, ...)

enableLogging(logger)

Logs debugging information to the console.

Signature:

exportdeclarefunctionenableLogging(logger:(message:string)=>unknown):any;

Parameters

Parameter	Type	Description
logger	(message: string) => unknown	A custom logger function to control how things get logged.

Returns:

any

function(parent, ...)

child(parent, path)

Gets aReference for the location at the specified relative path.

The relative path can either be a simple child name (for example, "ada") or a deeper slash-separated path (for example, "ada/name/first").

Signature:

exportdeclarefunctionchild(parent:DatabaseReference,path:string):DatabaseReference;

Parameters

Parameter	Type	Description
parent	DatabaseReference	The parent location.
path	string	A relative path from this location to the desired child location.

Returns:

DatabaseReference

The specified child location.

push(parent, value)

Generates a new child location using a unique key and returns itsReference.

This is the most common pattern for adding data to a collection of items.

If you provide a value topush(), the value is written to the generated location. If you don't pass a value, nothing is written to the database and the child remains empty (but you can use theReference elsewhere).

The unique keys generated bypush() are ordered by the current time, so the resulting list of items is chronologically sorted. The keys are also designed to be unguessable (they contain 72 random bits of entropy).

SeeAppend to a list of data. SeeThe 2^120 Ways to Ensure Unique Identifiers.

Signature:

exportdeclarefunctionpush(parent:DatabaseReference,value?:unknown):ThenableReference;

Parameters

Parameter	Type	Description
parent	DatabaseReference	The parent location.
value	unknown	Optional value to be written at the generated location.

Returns:

ThenableReference

CombinedPromise andReference; resolves when write is complete, but can be used immediately as theReference to the child location.

function(path, ...)

orderByChild(path)

Creates a newQueryConstraint that orders by the specified child key.

Queries can only order by one key at a time. CallingorderByChild() multiple times on the same query is an error.

Firebase queries allow you to order your data by any child key on the fly. However, if you know in advance what your indexes will be, you can define them via the .indexOn rule in your Security Rules for better performance. See thehttps://firebase.google.com/docs/database/security/indexing-data rule for more information.

You can read more aboutorderByChild() inSort data.

Signature:

exportdeclarefunctionorderByChild(path:string):QueryConstraint;

Parameters

Parameter	Type	Description
path	string	The path to order by.

Returns:

QueryConstraint

function(query, ...)

get(query)

Gets the most up-to-date result for this query.

Signature:

exportdeclarefunctionget(query:Query):Promise<DataSnapshot>;

Parameters

Parameter	Type	Description
query	Query	The query to run.

Returns:

Promise<DataSnapshot>

APromise which resolves to the resulting DataSnapshot if a value is available, or rejects if the client is unable to return a value (e.g., if the server is unreachable and there is nothing cached).

off(query, eventType, callback)

Detaches a callback previously attached with the correspondingon*() (onValue,onChildAdded) listener. Note: This is not the recommended way to remove a listener. Instead, please use the returned callback function from the respectiveon* callbacks.

Detach a callback previously attached withon*(). Callingoff() on a parent listener will not automatically remove listeners registered on child nodes,off() must also be called on any child listeners to remove the callback.

If a callback is not specified, all callbacks for the specified eventType will be removed. Similarly, if no eventType is specified, all callbacks for theReference will be removed.

Individual listeners can also be removed by invoking their unsubscribe callbacks.

Signature:

exportdeclarefunctionoff(query:Query,eventType?:EventType,callback?:(snapshot:DataSnapshot,previousChildName?:string|null)=>unknown):void;

Parameters

Parameter	Type	Description
query	Query	The query that the listener was registered with.
eventType	EventType	One of the following strings: "value", "child_added", "child_changed", "child_removed", or "child_moved." If omitted, all callbacks for the`Reference` will be removed.
callback	(snapshot:DataSnapshot, previousChildName?: string \| null) => unknown	The callback function that was passed to`on()` or`undefined` to remove all callbacks.

Returns:

void

onChildAdded(query, callback, cancelCallback)

Listens for data changes at a particular location.

This is the primary way to read data from a Database. Your callback will be triggered for the initial data and again whenever the data changes. Invoke the returned unsubscribe callback to stop receiving updates. SeeRetrieve Data on the Web for more details.

AnonChildAdded event will be triggered once for each initial child at this location, and it will be triggered again every time a new child is added. TheDataSnapshot passed into the callback will reflect the data for the relevant child. For ordering purposes, it is passed a second argument which is a string containing the key of the previous sibling child by sort order, ornull if it is the first child.

Signature:

exportdeclarefunctiononChildAdded(query:Query,callback:(snapshot:DataSnapshot,previousChildName?:string|null)=>unknown,cancelCallback?:(error:Error)=>unknown):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot, previousChildName?: string \| null) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
cancelCallback	(error: Error) => unknown	An optional callback that will be notified if your event subscription is ever canceled because your client does not have permission to read this data (or it had permission but has now lost it). This callback will be passed an`Error` object indicating why the failure occurred.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onChildAdded(query, callback, options)

Listens for data changes at a particular location.

Signature:

exportdeclarefunctiononChildAdded(query:Query,callback:(snapshot:DataSnapshot,previousChildName:string|null)=>unknown,options:ListenOptions):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot, previousChildName: string \| null) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
options	ListenOptions	An object that can be used to configure`onlyOnce`, which then removes the listener after its first invocation.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onChildAdded(query, callback, cancelCallback, options)

Listens for data changes at a particular location.

Signature:

exportdeclarefunctiononChildAdded(query:Query,callback:(snapshot:DataSnapshot,previousChildName:string|null)=>unknown,cancelCallback:(error:Error)=>unknown,options:ListenOptions):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot, previousChildName: string \| null) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
cancelCallback	(error: Error) => unknown	An optional callback that will be notified if your event subscription is ever canceled because your client does not have permission to read this data (or it had permission but has now lost it). This callback will be passed an`Error` object indicating why the failure occurred.
options	ListenOptions	An object that can be used to configure`onlyOnce`, which then removes the listener after its first invocation.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onChildChanged(query, callback, cancelCallback)

Listens for data changes at a particular location.

AnonChildChanged event will be triggered when the data stored in a child (or any of its descendants) changes. Note that a singlechild_changed event may represent multiple changes to the child. TheDataSnapshot passed to the callback will contain the new child contents. For ordering purposes, the callback is also passed a second argument which is a string containing the key of the previous sibling child by sort order, ornull if it is the first child.

Signature:

exportdeclarefunctiononChildChanged(query:Query,callback:(snapshot:DataSnapshot,previousChildName:string|null)=>unknown,cancelCallback?:(error:Error)=>unknown):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot, previousChildName: string \| null) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
cancelCallback	(error: Error) => unknown	An optional callback that will be notified if your event subscription is ever canceled because your client does not have permission to read this data (or it had permission but has now lost it). This callback will be passed an`Error` object indicating why the failure occurred.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onChildChanged(query, callback, options)

Listens for data changes at a particular location.

Signature:

exportdeclarefunctiononChildChanged(query:Query,callback:(snapshot:DataSnapshot,previousChildName:string|null)=>unknown,options:ListenOptions):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot, previousChildName: string \| null) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
options	ListenOptions	An object that can be used to configure`onlyOnce`, which then removes the listener after its first invocation.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onChildChanged(query, callback, cancelCallback, options)

Listens for data changes at a particular location.

Signature:

exportdeclarefunctiononChildChanged(query:Query,callback:(snapshot:DataSnapshot,previousChildName:string|null)=>unknown,cancelCallback:(error:Error)=>unknown,options:ListenOptions):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot, previousChildName: string \| null) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
cancelCallback	(error: Error) => unknown	An optional callback that will be notified if your event subscription is ever canceled because your client does not have permission to read this data (or it had permission but has now lost it). This callback will be passed an`Error` object indicating why the failure occurred.
options	ListenOptions	An object that can be used to configure`onlyOnce`, which then removes the listener after its first invocation.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onChildMoved(query, callback, cancelCallback)

Listens for data changes at a particular location.

AnonChildMoved event will be triggered when a child's sort order changes such that its position relative to its siblings changes. TheDataSnapshot passed to the callback will be for the data of the child that has moved. It is also passed a second argument which is a string containing the key of the previous sibling child by sort order, ornull if it is the first child.

Signature:

exportdeclarefunctiononChildMoved(query:Query,callback:(snapshot:DataSnapshot,previousChildName:string|null)=>unknown,cancelCallback?:(error:Error)=>unknown):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot, previousChildName: string \| null) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
cancelCallback	(error: Error) => unknown	An optional callback that will be notified if your event subscription is ever canceled because your client does not have permission to read this data (or it had permission but has now lost it). This callback will be passed an`Error` object indicating why the failure occurred.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onChildMoved(query, callback, options)

Listens for data changes at a particular location.

Signature:

exportdeclarefunctiononChildMoved(query:Query,callback:(snapshot:DataSnapshot,previousChildName:string|null)=>unknown,options:ListenOptions):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot, previousChildName: string \| null) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
options	ListenOptions	An object that can be used to configure`onlyOnce`, which then removes the listener after its first invocation.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onChildMoved(query, callback, cancelCallback, options)

Listens for data changes at a particular location.

Signature:

exportdeclarefunctiononChildMoved(query:Query,callback:(snapshot:DataSnapshot,previousChildName:string|null)=>unknown,cancelCallback:(error:Error)=>unknown,options:ListenOptions):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot, previousChildName: string \| null) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
cancelCallback	(error: Error) => unknown	An optional callback that will be notified if your event subscription is ever canceled because your client does not have permission to read this data (or it had permission but has now lost it). This callback will be passed an`Error` object indicating why the failure occurred.
options	ListenOptions	An object that can be used to configure`onlyOnce`, which then removes the listener after its first invocation.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onChildRemoved(query, callback, cancelCallback)

Listens for data changes at a particular location.

AnonChildRemoved event will be triggered once every time a child is removed. TheDataSnapshot passed into the callback will be the old data for the child that was removed. A child will get removed when either:

a client explicitly callsremove() on that child or one of its ancestors - a client callsset(null) on that child or one of its ancestors - that child has all of its children removed - there is a query in effect which now filters out the child (because it's sort order changed or the max limit was hit)

Signature:

exportdeclarefunctiononChildRemoved(query:Query,callback:(snapshot:DataSnapshot)=>unknown,cancelCallback?:(error:Error)=>unknown):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
cancelCallback	(error: Error) => unknown	An optional callback that will be notified if your event subscription is ever canceled because your client does not have permission to read this data (or it had permission but has now lost it). This callback will be passed an`Error` object indicating why the failure occurred.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onChildRemoved(query, callback, options)

Listens for data changes at a particular location.

a client explicitly callsremove() on that child or one of its ancestors - a client callsset(null) on that child or one of its ancestors - that child has all of its children removed - there is a query in effect which now filters out the child (because it's sort order changed or the max limit was hit)

Signature:

exportdeclarefunctiononChildRemoved(query:Query,callback:(snapshot:DataSnapshot)=>unknown,options:ListenOptions):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
options	ListenOptions	An object that can be used to configure`onlyOnce`, which then removes the listener after its first invocation.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onChildRemoved(query, callback, cancelCallback, options)

Listens for data changes at a particular location.

a client explicitly callsremove() on that child or one of its ancestors - a client callsset(null) on that child or one of its ancestors - that child has all of its children removed - there is a query in effect which now filters out the child (because it's sort order changed or the max limit was hit)

Signature:

exportdeclarefunctiononChildRemoved(query:Query,callback:(snapshot:DataSnapshot)=>unknown,cancelCallback:(error:Error)=>unknown,options:ListenOptions):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot and a string containing the key of the previous child, by sort order, or`null` if it is the first child.
cancelCallback	(error: Error) => unknown	An optional callback that will be notified if your event subscription is ever canceled because your client does not have permission to read this data (or it had permission but has now lost it). This callback will be passed an`Error` object indicating why the failure occurred.
options	ListenOptions	An object that can be used to configure`onlyOnce`, which then removes the listener after its first invocation.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onValue(query, callback, cancelCallback)

Listens for data changes at a particular location.

AnonValue event will trigger once with the initial data stored at this location, and then trigger again each time the data changes. TheDataSnapshot passed to the callback will be for the location at whichon() was called. It won't trigger until the entire contents has been synchronized. If the location has no data, it will be triggered with an emptyDataSnapshot (val() will returnnull).

Signature:

exportdeclarefunctiononValue(query:Query,callback:(snapshot:DataSnapshot)=>unknown,cancelCallback?:(error:Error)=>unknown):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot.
cancelCallback	(error: Error) => unknown	An optional callback that will be notified if your event subscription is ever canceled because your client does not have permission to read this data (or it had permission but has now lost it). This callback will be passed an`Error` object indicating why the failure occurred.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onValue(query, callback, options)

Listens for data changes at a particular location.

Signature:

exportdeclarefunctiononValue(query:Query,callback:(snapshot:DataSnapshot)=>unknown,options:ListenOptions):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot.
options	ListenOptions	An object that can be used to configure`onlyOnce`, which then removes the listener after its first invocation.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

onValue(query, callback, cancelCallback, options)

Listens for data changes at a particular location.

Signature:

exportdeclarefunctiononValue(query:Query,callback:(snapshot:DataSnapshot)=>unknown,cancelCallback:(error:Error)=>unknown,options:ListenOptions):Unsubscribe;

Parameters

Parameter	Type	Description
query	Query	The query to run.
callback	(snapshot:DataSnapshot) => unknown	A callback that fires when the specified event occurs. The callback will be passed a DataSnapshot.
cancelCallback	(error: Error) => unknown	An optional callback that will be notified if your event subscription is ever canceled because your client does not have permission to read this data (or it had permission but has now lost it). This callback will be passed an`Error` object indicating why the failure occurred.
options	ListenOptions	An object that can be used to configure`onlyOnce`, which then removes the listener after its first invocation.

Returns:

Unsubscribe

A function that can be invoked to remove the listener.

query(query, queryConstraints)

Creates a new immutable instance ofQuery that is extended to also include additional query constraints.

Signature:

exportdeclarefunctionquery(query:Query,...queryConstraints:QueryConstraint[]):Query;

Parameters

Parameter	Type	Description
query	Query	The Query instance to use as a base for the new constraints.
queryConstraints	QueryConstraint[]	The list of`QueryConstraint`s to apply.

Returns:

Query

Exceptions

if any of the provided query constraints cannot be combined with the existing or new constraints.

function(ref, ...)

onDisconnect(ref)

Returns anOnDisconnect object - seeEnabling Offline Capabilities in JavaScript for more information on how to use it.

Signature:

exportdeclarefunctiononDisconnect(ref:DatabaseReference):OnDisconnect;

Parameters

Parameter	Type	Description
ref	DatabaseReference	The reference to add OnDisconnect triggers for.

Returns:

OnDisconnect

remove(ref)

Removes the data at this Database location.

Any data at child locations will also be deleted.

The effect of the remove will be visible immediately and the corresponding event 'value' will be triggered. Synchronization of the remove to the Firebase servers will also be started, and the returned Promise will resolve when complete. If provided, the onComplete callback will be called asynchronously after synchronization has finished.

Signature:

exportdeclarefunctionremove(ref:DatabaseReference):Promise<void>;

Parameters

Parameter	Type	Description
ref	DatabaseReference	The location to remove.

Returns:

Promise<void>

Resolves when remove on server is complete.

runTransaction(ref, transactionUpdate, options)

Atomically modifies the data at this location.

Atomically modify the data at this location. Unlike a normalset(), which just overwrites the data regardless of its previous value,runTransaction() is used to modify the existing value to a new value, ensuring there are no conflicts with other clients writing to the same location at the same time.

To accomplish this, you passrunTransaction() an update function which is used to transform the current value into a new value. If another client writes to the location before your new value is successfully written, your update function will be called again with the new current value, and the write will be retried. This will happen repeatedly until your write succeeds without conflict or you abort the transaction by not returning a value from your update function.

Note: Modifying data withset() will cancel any pending transactions at that location, so extreme care should be taken if mixingset() andrunTransaction() to update the same data.Note: When using transactions with Security and Firebase Rules in place, be aware that a client needs.read access in addition to.write access in order to perform a transaction. This is because the client-side nature of transactions requires the client to read the data in order to transactionally update it.

Signature:

exportdeclarefunctionrunTransaction(ref:DatabaseReference,transactionUpdate:(currentData:any)=>unknown,options?:TransactionOptions):Promise<TransactionResult>;

Parameters

Parameter	Type	Description
ref	DatabaseReference	The location to atomically modify.
transactionUpdate	(currentData: any) => unknown	A developer-supplied function which will be passed the current data stored at this location (as a JavaScript object). The function should return the new value it would like written (as a JavaScript object). If`undefined` is returned (i.e. you return with no arguments) the transaction will be aborted and the data at this location will not be modified.
options	TransactionOptions	An options object to configure transactions.

Returns:

Promise<TransactionResult>

APromise that can optionally be used instead of theonComplete callback to handle success and failure.

set(ref, value)

Writes data to this Database location.

This will overwrite any data at this location and all child locations.

The effect of the write will be visible immediately, and the corresponding events ("value", "child_added", etc.) will be triggered. Synchronization of the data to the Firebase servers will also be started, and the returned Promise will resolve when complete. If provided, theonComplete callback will be called asynchronously after synchronization has finished.

Passingnull for the new value is equivalent to callingremove(); namely, all data at this location and all child locations will be deleted.

set() will remove any priority stored at this location, so if priority is meant to be preserved, you need to usesetWithPriority() instead.

Note that modifying data withset() will cancel any pending transactions at that location, so extreme care should be taken if mixingset() andtransaction() to modify the same data.

A singleset() will generate a single "value" event at the location where theset() was performed.

Signature:

exportdeclarefunctionset(ref:DatabaseReference,value:unknown):Promise<void>;

Parameters

Parameter	Type	Description
ref	DatabaseReference	The location to write to.
value	unknown	The value to be written (string, number, boolean, object, array, or null).

Returns:

Promise<void>

Resolves when write to server is complete.

setPriority(ref, priority)

Sets a priority for the data at this Database location.

Applications need not use priority but can order collections by ordinary properties (seeSorting and filtering data ).

Signature:

exportdeclarefunctionsetPriority(ref:DatabaseReference,priority:string|number|null):Promise<void>;

Parameters

Parameter	Type	Description
ref	DatabaseReference	The location to write to.
priority	string \| number \| null	The priority to be written (string, number, or null).

Returns:

Promise<void>

Resolves when write to server is complete.

setWithPriority(ref, value, priority)

Writes data the Database location. Likeset() but also specifies the priority for that data.

Applications need not use priority but can order collections by ordinary properties (seeSorting and filtering data ).

Signature:

exportdeclarefunctionsetWithPriority(ref:DatabaseReference,value:unknown,priority:string|number|null):Promise<void>;

Parameters

Parameter	Type	Description
ref	DatabaseReference	The location to write to.
value	unknown	The value to be written (string, number, boolean, object, array, or null).
priority	string \| number \| null	The priority to be written (string, number, or null).

Returns:

Promise<void>

Resolves when write to server is complete.

update(ref, values)

Writes multiple values to the Database at once.

Thevalues argument contains multiple property-value pairs that will be written to the Database together. Each child property can either be a simple property (for example, "name") or a relative path (for example, "name/first") from the current location to the data to update.

As opposed to theset() method,update() can be use to selectively update only the referenced properties at the current location (instead of replacing all the child properties at the current location).

The effect of the write will be visible immediately, and the corresponding events ('value', 'child_added', etc.) will be triggered. Synchronization of the data to the Firebase servers will also be started, and the returned Promise will resolve when complete. If provided, theonComplete callback will be called asynchronously after synchronization has finished.

A singleupdate() will generate a single "value" event at the location where theupdate() was performed, regardless of how many children were modified.

Note that modifying data withupdate() will cancel any pending transactions at that location, so extreme care should be taken if mixingupdate() andtransaction() to modify the same data.

Passingnull toupdate() will remove the data at this location.

SeeIntroducing multi-location updates and more.

Signature:

exportdeclarefunctionupdate(ref:DatabaseReference,values:object):Promise<void>;

Parameters

Parameter	Type	Description
ref	DatabaseReference	The location to write to.
values	object	Object containing multiple values.

Returns:

Promise<void>

Resolves when update on server is complete.

function(value, ...)

endAt(value, key)

Creates aQueryConstraint with the specified ending point.

UsingstartAt(),startAfter(),endBefore(),endAt() andequalTo() allows you to choose arbitrary starting and ending points for your queries.

The ending point is inclusive, so children with exactly the specified value will be included in the query. The optional key argument can be used to further limit the range of the query. If it is specified, then children that have exactly the specified value must also have a key name less than or equal to the specified key.

You can read more aboutendAt() inFiltering data.

Signature:

exportdeclarefunctionendAt(value:number|string|boolean|null,key?:string):QueryConstraint;

Parameters

Parameter	Type	Description
value	number \| string \| boolean \| null	The value to end at. The argument type depends on which`orderBy()` function was used in this query. Specify a value that matches the`orderBy``()` type. When used in combination with`orderByKey()`, the value must be a string.
key	string	The child key to end at, among the children with the previously specified priority. This argument is only allowed if ordering by child, value, or priority.

Returns:

QueryConstraint

endBefore(value, key)

Creates aQueryConstraint with the specified ending point (exclusive).

UsingstartAt(),startAfter(),endBefore(),endAt() andequalTo() allows you to choose arbitrary starting and ending points for your queries.

The ending point is exclusive. If only a value is provided, children with a value less than the specified value will be included in the query. If a key is specified, then children must have a value less than or equal to the specified value and a key name less than the specified key.

Signature:

exportdeclarefunctionendBefore(value:number|string|boolean|null,key?:string):QueryConstraint;

Parameters

Parameter	Type	Description
value	number \| string \| boolean \| null	The value to end before. The argument type depends on which`orderBy()` function was used in this query. Specify a value that matches the`orderBy``()` type. When used in combination with`orderByKey()`, the value must be a string.
key	string	The child key to end before, among the children with the previously specified priority. This argument is only allowed if ordering by child, value, or priority.

Returns:

QueryConstraint

equalTo(value, key)

Creates aQueryConstraint that includes children that match the specified value.

UsingstartAt(),startAfter(),endBefore(),endAt() andequalTo() allows you to choose arbitrary starting and ending points for your queries.

The optional key argument can be used to further limit the range of the query. If it is specified, then children that have exactly the specified value must also have exactly the specified key as their key name. This can be used to filter result sets with many matches for the same value.

You can read more aboutequalTo() inFiltering data.

Signature:

exportdeclarefunctionequalTo(value:number|string|boolean|null,key?:string):QueryConstraint;

Parameters

Parameter	Type	Description
value	number \| string \| boolean \| null	The value to match for. The argument type depends on which`orderBy()` function was used in this query. Specify a value that matches the`orderBy``()` type. When used in combination with`orderByKey()`, the value must be a string.
key	string	The child key to start at, among the children with the previously specified priority. This argument is only allowed if ordering by child, value, or priority.

Returns:

QueryConstraint

startAfter(value, key)

Creates aQueryConstraint with the specified starting point (exclusive).

UsingstartAt(),startAfter(),endBefore(),endAt() andequalTo() allows you to choose arbitrary starting and ending points for your queries.

The starting point is exclusive. If only a value is provided, children with a value greater than the specified value will be included in the query. If a key is specified, then children must have a value greater than or equal to the specified value and a a key name greater than the specified key.

Signature:

exportdeclarefunctionstartAfter(value:number|string|boolean|null,key?:string):QueryConstraint;

Parameters

Parameter	Type	Description
value	number \| string \| boolean \| null	The value to start after. The argument type depends on which`orderBy()` function was used in this query. Specify a value that matches the`orderBy``()` type. When used in combination with`orderByKey()`, the value must be a string.
key	string	The child key to start after. This argument is only allowed if ordering by child, value, or priority.

Returns:

QueryConstraint

startAt(value, key)

Creates aQueryConstraint with the specified starting point.

UsingstartAt(),startAfter(),endBefore(),endAt() andequalTo() allows you to choose arbitrary starting and ending points for your queries.

The starting point is inclusive, so children with exactly the specified value will be included in the query. The optional key argument can be used to further limit the range of the query. If it is specified, then children that have exactly the specified value must also have a key name greater than or equal to the specified key.

You can read more aboutstartAt() inFiltering data.

Signature:

exportdeclarefunctionstartAt(value?:number|string|boolean|null,key?:string):QueryConstraint;

Parameters

Parameter	Type	Description
value	number \| string \| boolean \| null	The value to start at. The argument type depends on which`orderBy()` function was used in this query. Specify a value that matches the`orderBy``()` type. When used in combination with`orderByKey()`, the value must be a string.
key	string	The child key to start at. This argument is only allowed if ordering by child, value, or priority.

Returns:

QueryConstraint

EventType

One of the following strings: "value", "child_added", "child_changed", "child_removed", or "child_moved."

Signature:

exportdeclaretypeEventType='value'|'child_added'|'child_changed'|'child_moved'|'child_removed';

QueryConstraintType

Describes the different query constraints available in this SDK.

Signature:

exportdeclaretypeQueryConstraintType='endAt'|'endBefore'|'startAt'|'startAfter'|'limitToFirst'|'limitToLast'|'orderByChild'|'orderByKey'|'orderByPriority'|'orderByValue'|'equalTo';

Unsubscribe

A callback that can invoked to remove a listener.

Signature:

exportdeclaretypeUnsubscribe=()=>void;

Except as otherwise noted, the content of this page is licensed under theCreative Commons Attribution 4.0 License, and code samples are licensed under theApache 2.0 License. For details, see theGoogle Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.

Last updated 2024-08-01 UTC.

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database package Stay organized with collections Save and categorize content based on your preferences.

Functions

Classes

Interfaces

Type Aliases

function(app, ...)

getDatabase(app, url)

Parameters

function(db, ...)

connectDatabaseEmulator(db, host, port, options)

Parameters

goOffline(db)

Parameters

goOnline(db)

Parameters

ref(db, path)

Parameters

refFromURL(db, url)

Parameters

function()

forceLongPolling()

forceWebSockets()

orderByKey()

orderByPriority()

orderByValue()

serverTimestamp()

function(delta, ...)

increment(delta)

Parameters

function(enabled, ...)

enableLogging(enabled, persistent)

Parameters

function(limit, ...)

limitToFirst(limit)

Parameters

limitToLast(limit)

Parameters

function(logger, ...)

enableLogging(logger)

Parameters

function(parent, ...)

child(parent, path)

Parameters

push(parent, value)

Parameters

function(path, ...)

orderByChild(path)

Parameters

function(query, ...)

get(query)

Parameters

off(query, eventType, callback)

Parameters

onChildAdded(query, callback, cancelCallback)

Parameters

onChildAdded(query, callback, options)

Parameters

onChildAdded(query, callback, cancelCallback, options)

Parameters

onChildChanged(query, callback, cancelCallback)

Parameters

onChildChanged(query, callback, options)

Parameters

onChildChanged(query, callback, cancelCallback, options)

Parameters

onChildMoved(query, callback, cancelCallback)

Parameters

onChildMoved(query, callback, options)

Parameters

onChildMoved(query, callback, cancelCallback, options)

Parameters

onChildRemoved(query, callback, cancelCallback)

Parameters

onChildRemoved(query, callback, options)

Parameters

onChildRemoved(query, callback, cancelCallback, options)

Parameters

onValue(query, callback, cancelCallback)

Parameters

database package