key

parent

ref

Inherited fromQuery.ref

root

child

• child(path: string):Reference

• Gets aReference for the location at the specified relative path.

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

  example

  var usersRef = firebase.database().ref('users');var adaRef = usersRef.child('ada');var adaFirstNameRef = adaRef.child('name/first');var path = adaFirstNameRef.toString();// path is now 'https://sample-app.firebaseio.com/users/ada/name/first'

  Parameters

  • path:string

    A relative path from this location to the desired childlocation.

  ReturnsReference

  The specified child location.

endAt

• endAt(value: number |string |boolean |null, key?: string):Query

• Inherited fromQuery.endAt

  Creates aQuery 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 valuewill be included in the query. The optional key argument can be used tofurther limit the range of the query. If it is specified, then children thathave exactly the specified value must also have a key name less than or equalto the specified key.

  You can read more aboutendAt() in Filtering data.

  example

  // Find all dinosaurs whose names come before Pterodactyl lexicographically.// Include Pterodactyl in the result.var ref = firebase.database().ref("dinosaurs");ref.orderByKey().endAt("pterodactyl").on("child_added",function(snapshot){console.log(snapshot.key);});

  Parameters

  • value:number |string |boolean |null

    The value to end at. The argumenttype depends on whichorderBy*() function was used in this query.Specify a value that matches theorderBy*() type. When used incombination withorderByKey(), the value must be a string.

  • Optional key:string

    The child key to end at, among the children with thepreviously specified priority. This argument is only allowed if ordering bychild, value, or priority.

  ReturnsQuery

endBefore

• endBefore(value: number |string |boolean |null, key?: string):Query

• Inherited fromQuery.endBefore

  Creates aQuery 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, childrenwith a value less than the specified value will be included in the query.If a key is specified, then children must have a value lesss than or equalto the specified value and a a key name less than the specified key.

  example

  // Find all dinosaurs whose names come before Pterodactyl lexicographically.// Do not include Pterodactyl in the result.var ref = firebase.database().ref("dinosaurs");ref.orderByKey().endBefore("pterodactyl").on("child_added",function(snapshot){console.log(snapshot.key);});@param value The value to end before. The argument  type depends on which`orderBy*()`functionwasusedinthisquery.Specifyavaluethatmatchesthe `orderBy*()`type.Whenusedincombinationwith `orderByKey()`,thevaluemustbeastring.@paramkeyThechildkeytoendbefore,amongthechildrenwiththepreviouslyspecifiedpriority.Thisargumentisonlyallowediforderingbychild,value,orpriority.

  Parameters

  • value:number |string |boolean |null

  • Optional key:string

  ReturnsQuery

equalTo

• equalTo(value: number |string |boolean |null, key?: string):Query

• Inherited fromQuery.equalTo

  Creates aQuery 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 thequery. If it is specified, then children that have exactly the specifiedvalue must also have exactly the specified key as their key name. This can beused to filter result sets with many matches for the same value.

  You can read more aboutequalTo() in Filtering data.

  example

  // Find all dinosaurs whose height is exactly 25 meters.var ref = firebase.database().ref("dinosaurs");ref.orderByChild("height").equalTo(25).on("child_added",function(snapshot){console.log(snapshot.key);});

  Parameters

  • value:number |string |boolean |null

    The value to match for. Theargument type depends on whichorderBy*() function was used in thisquery. Specify a value that matches theorderBy*() type. When used incombination withorderByKey(), the value must be a string.

  • Optional key:string

    The child key to start at, among the children with thepreviously specified priority. This argument is only allowed if ordering bychild, value, or priority.

  ReturnsQuery

get

• get():Promise<DataSnapshot>

• Inherited fromQuery.get

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

  ReturnsPromise<DataSnapshot>

  A promise which resolves to the resulting DataSnapshot ifa value is available, or rejects if the client is unable to returna value (e.g., if the server is unreachable and there is nothingcached).

isEqual

• isEqual(other: Query |null):boolean

• Inherited fromQuery.isEqual

  Returns whether or not the current and provided queries represent the samelocation, have the same query parameters, and are from the same instance offirebase.app.App.

  TwoReference objects are equivalent if they represent the same locationand are from the same instance offirebase.app.App.

  TwoQuery objects are equivalent if they represent the same location, havethe same query parameters, and are from the same instance offirebase.app.App. Equivalent queries share the same sort order, limits, andstarting and ending points.

  example

  var rootRef = firebase.database.ref();var usersRef = rootRef.child("users");usersRef.isEqual(rootRef);// falseusersRef.isEqual(rootRef.child("users"));// trueusersRef.parent.isEqual(rootRef);// true

  example

  var rootRef = firebase.database.ref();var usersRef = rootRef.child("users");var usersQuery = usersRef.limitToLast(10);usersQuery.isEqual(usersRef);// falseusersQuery.isEqual(usersRef.limitToLast(10));// trueusersQuery.isEqual(rootRef.limitToLast(10));// falseusersQuery.isEqual(usersRef.orderByKey().limitToLast(10));// false

  Parameters

  • other:Query |null

    The query to compare against.

  Returnsboolean

  Whether or not the current and provided queries areequivalent.

limitToFirst

• limitToFirst(limit: number):Query

• Inherited fromQuery.limitToFirst

  Generates a newQuery limited to the first specific number of children.

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

  You can read more aboutlimitToFirst() in Filtering data.

  example

  // Find the two shortest dinosaurs.var ref = firebase.database().ref("dinosaurs");ref.orderByChild("height").limitToFirst(2).on("child_added",function(snapshot){// This will be called exactly two times (unless there are less than two// dinosaurs in the Database).// It will also get fired again if one of the first two dinosaurs is// removed from the data set, as a new dinosaur will now be the second// shortest.console.log(snapshot.key);});

  Parameters

  • limit:number

    The maximum number of nodes to include in this query.

  ReturnsQuery

limitToLast

• limitToLast(limit: number):Query

• Inherited fromQuery.limitToLast

  Generates a newQuery object limited to the last specific number ofchildren.

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

  You can read more aboutlimitToLast() in Filtering data.

  example

  // Find the two heaviest dinosaurs.var ref = firebase.database().ref("dinosaurs");ref.orderByChild("weight").limitToLast(2).on("child_added",function(snapshot){// This callback will be triggered exactly two times, unless there are// fewer than two dinosaurs stored in the Database. It will also get fired// for every new, heavier dinosaur that gets added to the data set.console.log(snapshot.key);});

  Parameters

  • limit:number

    The maximum number of nodes to include in this query.

  ReturnsQuery

off

• off(eventType?: EventType, callback?: (a: DataSnapshot, b?: string |null) =>any, context?: Object |null):void

• Inherited fromQuery.off

  Detaches a callback previously attached withon().

  Detach a callback previously attached withon(). Note that ifon() wascalled multiple times with the same eventType and callback, the callbackwill be called multiple times for each event, andoff() must be calledmultiple times to remove the callback. Callingoff() on a parent listenerwill 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 eventTypewill be removed. Similarly, if no eventType is specified, all callbacksfor theReference will be removed.

  example

  var onValueChange =function(dataSnapshot){  ... };ref.on('value', onValueChange);ref.child('meta-data').on('child_added', onChildAdded);// Sometime later...ref.off('value', onValueChange);// You must also call off() for any child listeners on ref// to cancel those callbacksref.child('meta-data').off('child_added', onValueAdded);

  example

  // Or you can save a line of code by using an inline function// and on()'s return value.var onValueChange = ref.on('value',function(dataSnapshot){ ... });// Sometime later...ref.off('value', onValueChange);

  Parameters

  • Optional eventType:EventType

    One of the following strings: "value","child_added", "child_changed", "child_removed", or "child_moved." Ifomitted, all callbacks for theReference will be removed.

  • Optional callback:(a:DataSnapshot, b?:string |null) =>any

    The callback function that was passed toon() orundefined to remove all callbacks.

    • • (a:DataSnapshot, b?:string |null):any

      • Parameters

        • a:DataSnapshot

        • Optional b:string |null

        Returnsany

  • Optional context:Object |null

    The context that was passed toon().

  Returnsvoid

on

• on(eventType: EventType, callback: (a: DataSnapshot, b?: string |null) =>any, cancelCallbackOrContext?: ((a: Error) =>any) |Object |null, context?: Object |null):(a: DataSnapshot |null, b?: string |null) =>any

• Inherited fromQuery.on

  Listens for data changes at a particular location.

  This is the primary way to read data from a Database. Your callbackwill be triggered for the initial data and again whenever the data changes.Useoff( ) to stop receiving updates. See Retrieve Data on the Webfor more details.

  value event

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

  child_added event

  This 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 therelevant child. For ordering purposes, it is passed a second argument whichis a string containing the key of the previous sibling child by sort order,ornull if it is the first child.

  child_removed event

  This event will be triggered once every time a child is removed. TheDataSnapshot passed into the callback will be the old data for the childthat 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'ssort order changed or the max limit was hit)

  child_changed event

  This event will be triggered when the data stored in a child (or any of itsdescendants) changes. Note that a singlechild_changed event may representmultiple changes to the child. TheDataSnapshot passed to the callback willcontain the new child contents. For ordering purposes, the callback is alsopassed a second argument which is a string containing the key of the previoussibling child by sort order, ornull if it is the first child.

  child_moved event

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

  example

  Handle a new value:

  ref.on('value',function(dataSnapshot){  ...});

  example

  Handle a new child:

  ref.on('child_added',function(childSnapshot, prevChildKey){  ...});

  example

  Handle child removal:

  ref.on('child_removed',function(oldChildSnapshot){  ...});

  example

  Handle child data changes:

  ref.on('child_changed',function(childSnapshot, prevChildKey){  ...});

  example

  Handle child ordering changes:

  ref.on('child_moved',function(childSnapshot, prevChildKey){  ...});

  Parameters

  • eventType:EventType

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

  • callback:(a:DataSnapshot, b?:string |null) =>any

    Acallback that fires when the specified event occurs. The callback will bepassed a DataSnapshot. For ordering purposes, "child_added","child_changed", and "child_moved" will also be passed a string containingthe key of the previous child, by sort order, ornull if it is thefirst child.

    • • (a:DataSnapshot, b?:string |null):any

      • Parameters

        • a:DataSnapshot

        • Optional b:string |null

        Returnsany

  • Optional cancelCallbackOrContext:((a:Error) =>any) |Object |null

    An optionalcallback that will be notified if your event subscription is ever canceledbecause your client does not have permission to read this data (or it hadpermission but has now lost it). This callback will be passed anErrorobject indicating why the failure occurred.

  • Optional context:Object |null

    If provided, this object will be used asthiswhen calling your callback(s).

  Returns(a:DataSnapshot |null, b?:string |null) =>any

  The providedcallback function is returned unmodified. This is just for convenience ifyou want to pass an inline function toon() but store the callbackfunction for later passing tooff().

  • • (a:DataSnapshot |null, b?:string |null):any

    • Parameters

      • a:DataSnapshot |null

      • Optional b:string |null

      Returnsany

onDisconnect

• onDisconnect():OnDisconnect

• Returns anOnDisconnect object - see Enabling Offline Capabilities in JavaScript for more information on howto use it.

  ReturnsOnDisconnect

once

• once(eventType: EventType, successCallback?: (a: DataSnapshot, b?: string |null) =>any, failureCallbackOrContext?: ((a: Error) =>void) |Object |null, context?: Object |null):Promise<DataSnapshot>

• Inherited fromQuery.once

  Listens for exactly one event of the specified event type, and then stopslistening.

  This is equivalent to callingon(), andthen callingoff() inside the callbackfunction. Seeon() for details on theevent types.

  example

  // Basic usage of .once() to read the data located at ref.ref.once('value')  .then(function(dataSnapshot){// handle read data.  });

  Parameters

  • eventType:EventType

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

  • Optional successCallback:(a:DataSnapshot, b?:string |null) =>any

    Acallback that fires when the specified event occurs. The callback will bepassed a DataSnapshot. For ordering purposes, "child_added","child_changed", and "child_moved" will also be passed a string containingthe key of the previous child by sort order, ornull if it is thefirst child.

    • • (a:DataSnapshot, b?:string |null):any

      • Parameters

        • a:DataSnapshot

        • Optional b:string |null

        Returnsany

  • Optional failureCallbackOrContext:((a:Error) =>void) |Object |null

    An optionalcallback that will be notified if your client does not have permission toread the data. This callback will be passed anError object indicatingwhy the failure occurred.

  • Optional context:Object |null

    If provided, this object will be used asthiswhen calling your callback(s).

  ReturnsPromise<DataSnapshot>

orderByChild

• orderByChild(path: string):Query

• Inherited fromQuery.orderByChild

  Generates a newQuery object ordered 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 definethem via the .indexOn rule in your Security Rules for better performance. Seethe.indexOn rule for more information.

  You can read more aboutorderByChild() in Sort data.

  example

  var ref = firebase.database().ref("dinosaurs");ref.orderByChild("height").on("child_added",function(snapshot){console.log(snapshot.key +" was " + snapshot.val().height +" m tall");});

  Parameters

  • path:string

  ReturnsQuery

orderByKey

• orderByKey():Query

• Inherited fromQuery.orderByKey

  Generates a newQuery object ordered by key.

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

  You can read more aboutorderByKey() in Sort data.

  example

  var ref = firebase.database().ref("dinosaurs");ref.orderByKey().on("child_added",function(snapshot){console.log(snapshot.key);});

  ReturnsQuery

orderByPriority

• orderByPriority():Query

• Inherited fromQuery.orderByPriority

  Generates a newQuery object ordered by priority.

  Applications need not use priority but can order collections byordinary properties (see Sort data for alternatives to priority.

  ReturnsQuery

orderByValue

• orderByValue():Query

• Inherited fromQuery.orderByValue

  Generates a newQuery object ordered by value.

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

  You can read more aboutorderByValue() in Sort data.

  example

  var scoresRef = firebase.database().ref("scores");scoresRef.orderByValue().limitToLast(3).on("value",function(snapshot){  snapshot.forEach(function(data){console.log("The " + data.key +" score is " + data.val());  });});

  ReturnsQuery

push

• push(value?: any, onComplete?: (a: Error |null) =>any):ThenableReference

• 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 thegenerated location. If you don't pass a value, nothing is written to thedatabase and the child remains empty (but you can use theReferenceelsewhere).

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

  See Append to a list of data
  See The 2^120 Ways to Ensure Unique Identifiers

  example

  var messageListRef = firebase.database().ref('message_list');var newMessageRef = messageListRef.push();newMessageRef.set({'user_id':'ada','text':'The Analytical Engine weaves algebraical patterns just as the Jacquard loom weaves flowers and leaves.'});// We've appended a new message to the message_list location.var path = newMessageRef.toString();// path will be something like// 'https://sample-app.firebaseio.com/message_list/-IKo28nwJLH0Nc5XeFmj'

  Parameters

  • Optional value:any

    Optional value to be written at the generated location.

  • Optional onComplete:(a:Error |null) =>any

    Callback called when write to server iscomplete.

    • • (a:Error |null):any

      • Parameters

        • a:Error |null

        Returnsany

  ReturnsThenableReference

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

remove

• remove(onComplete?: (a: Error |null) =>void):Promise<void>

• 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 correspondingevent 'value' will be triggered. Synchronization of the remove to theFirebase servers will also be started, and the returned Promise will resolvewhen complete. If provided, the onComplete callback will be calledasynchronously after synchronization has finished.

  example

  var adaRef = firebase.database().ref('users/ada');adaRef.remove()  .then(function(){console.log("Remove succeeded.")  })  .catch(function(error){console.log("Remove failed: " + error.message)  });

  Parameters

  • Optional onComplete:(a:Error |null) =>void

    Callback called when write to server iscomplete.

    • • (a:Error |null):void

      • Parameters

        • a:Error |null

        Returnsvoid

  ReturnsPromise<void>

  Resolves when remove on server is complete.

set

• set(value: any, onComplete?: (a: Error |null) =>void):Promise<void>

• 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 correspondingevents ("value", "child_added", etc.) will be triggered. Synchronization ofthe data to the Firebase servers will also be started, and the returnedPromise will resolve when complete. If provided, theonComplete callbackwill 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 ismeant to be preserved, you need to usesetWithPriority() instead.

  Note that modifying data withset() will cancel any pending transactionsat 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 wheretheset() was performed.

  example

  var adaNameRef = firebase.database().ref('users/ada/name');adaNameRef.child('first').set('Ada');adaNameRef.child('last').set('Lovelace');// We've written 'Ada' to the Database location storing Ada's first name,// and 'Lovelace' to the location storing her last name.

  example

  adaNameRef.set({first:'Ada',last:'Lovelace' });// Exact same effect as the previous example, except we've written// Ada's first and last name simultaneously.

  example

  adaNameRef.set({first:'Ada',last:'Lovelace' })  .then(function(){console.log('Synchronization succeeded');  })  .catch(function(error){console.log('Synchronization failed');  });// Same as the previous example, except we will also log a message// when the data has finished synchronizing.

  Parameters

  • value:any

    The value to be written (string, number, boolean, object,array, or null).

  • Optional onComplete:(a:Error |null) =>void

    Callback called when write to server iscomplete.

    • • (a:Error |null):void

      • Parameters

        • a:Error |null

        Returnsvoid

  ReturnsPromise<void>

  Resolves when write to server is complete.

setPriority

• setPriority(priority: string |number |null, onComplete: (a: Error |null) =>void):Promise<void>

• Sets a priority for the data at this Database location.

  Applications need not use priority but can order collections byordinary properties (see Sorting and filtering data).

  Parameters

  • priority:string |number |null

  • onComplete:(a:Error |null) =>void

    • • (a:Error |null):void

      • Parameters

        • a:Error |null

        Returnsvoid

  ReturnsPromise<void>

setWithPriority

• setWithPriority(newVal: any, newPriority: string |number |null, onComplete?: (a: Error |null) =>void):Promise<void>

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

  Applications need not use priority but can order collections byordinary properties (see Sorting and filtering data).

  Parameters

  • newVal:any

  • newPriority:string |number |null

  • Optional onComplete:(a:Error |null) =>void

    • • (a:Error |null):void

      • Parameters

        • a:Error |null

        Returnsvoid

  ReturnsPromise<void>

startAfter

• startAfter(value: number |string |boolean |null, key?: string):Query

• Inherited fromQuery.startAfter

  Creates aQuery 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, childrenwith 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 equalto the specified value and a a key name greater than the specified key.

  example

  // Find all dinosaurs that are more than three meters tall.var ref = firebase.database().ref("dinosaurs");ref.orderByChild("height").startAfter(3).on("child_added",function(snapshot){console.log(snapshot.key)});

  Parameters

  • value:number |string |boolean |null

    The value to start after. The argumenttype depends on whichorderBy*() function was used in this query.Specify a value that matches theorderBy*() type. When used incombination withorderByKey(), the value must be a string.

  • Optional key:string

    The child key to start after. This argument is only allowedif ordering by child, value, or priority.

  ReturnsQuery

startAt

• startAt(value: number |string |boolean |null, key?: string):Query

• Inherited fromQuery.startAt

  Creates aQuery 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 valuewill be included in the query. The optional key argument can be used tofurther limit the range of the query. If it is specified, then children thathave exactly the specified value must also have a key name greater than orequal to the specified key.

  You can read more aboutstartAt() in Filtering data.

  example

  // Find all dinosaurs that are at least three meters tall.var ref = firebase.database().ref("dinosaurs");ref.orderByChild("height").startAt(3).on("child_added",function(snapshot){console.log(snapshot.key)});

  Parameters

  • value:number |string |boolean |null

    The value to start at. The argumenttype depends on whichorderBy*() function was used in this query.Specify a value that matches theorderBy*() type. When used incombination withorderByKey(), the value must be a string.

  • Optional key:string

    The child key to start at. This argument is only allowedif ordering by child, value, or priority.

  ReturnsQuery

toJSON

• toJSON():Object

• Inherited fromQuery.toJSON

  Returns a JSON-serializable representation of this object.

  ReturnsObject

  A JSON-serializable representation of this object.

toString

• toString():string

• Inherited fromQuery.toString

  Gets the absolute URL for this location.

  ThetoString() method returns a URL that is ready to be put into a browser,curl command, or afirebase.database().refFromURL() call. Since all ofthose expect the URL to be url-encoded,toString() returns an encoded URL.

  Append '.json' to the returned URL when typed into a browser to downloadJSON-formatted data. If the location is secured (that is, not publiclyreadable), you will get a permission-denied error.

  example

  // Calling toString() on a root Firebase reference returns the URL where its// data is stored within the Database:var rootRef = firebase.database().ref();var rootUrl = rootRef.toString();// rootUrl === "https://sample-app.firebaseio.com/".// Calling toString() at a deeper Firebase reference returns the URL of that// deep path within the Database:var adaRef = rootRef.child('users/ada');var adaURL = adaRef.toString();// adaURL === "https://sample-app.firebaseio.com/users/ada".

  Returnsstring

  The absolute URL for this location.

transaction

• transaction(transactionUpdate: (a: any) =>any, onComplete?: (a: Error |null, b: boolean, c: DataSnapshot |null) =>void, applyLocally?: boolean):Promise<TransactionResult>

• Atomically modifies the data at this location.

  Atomically modify the data at this location. Unlike a normalset(), whichjust overwrites the data regardless of its previous value,transaction() isused to modify the existing value to a new value, ensuring there are noconflicts with other clients writing to the same location at the same time.

  To accomplish this, you passtransaction() an update function which is usedto transform the current value into a new value. If another client writes tothe location before your new value is successfully written, your updatefunction will be called again with the new current value, and the write willbe retried. This will happen repeatedly until your write succeeds withoutconflict or you abort the transaction by not returning a value from yourupdate function.

  Note: Modifying data withset() will cancel any pending transactions atthat location, so extreme care should be taken if mixingset() andtransaction() to update the same data.

  Note: When using transactions with Security and Firebase Rules in place, beaware that a client needs.read access in addition to.write access inorder to perform a transaction. This is because the client-side nature oftransactions requires the client to read the data in order to transactionallyupdate it.

  example

  // Increment Ada's rank by 1.var adaRankRef = firebase.database().ref('users/ada/rank');adaRankRef.transaction(function(currentRank){// If users/ada/rank has never been set, currentRank will be `null`.return currentRank +1;});

  example

  // Try to create a user for ada, but only if the user id 'ada' isn't// already takenvar adaRef = firebase.database().ref('users/ada');adaRef.transaction(function(currentData){if (currentData ===null) {return {name: {first:'Ada',last:'Lovelace' } };  }else {console.log('User ada already exists.');return;// Abort the transaction.  }},function(error, committed, snapshot){if (error) {console.log('Transaction failed abnormally!', error);  }elseif (!committed) {console.log('We aborted the transaction (because ada already exists).');  }else {console.log('User ada added!');  }console.log("Ada's data: ", snapshot.val());});

  Parameters

  • transactionUpdate:(a:any) =>any

    A developer-supplied function whichwill be passed the current data stored at this location (as a JavaScriptobject). The function should return the new value it would like written (asa JavaScript object). Ifundefined is returned (i.e. you return with noarguments) the transaction will be aborted and the data at this locationwill not be modified.

    • • (a:any):any

      • Parameters

        • a:any

        Returnsany

  • Optional onComplete:(a:Error |null, b:boolean, c:DataSnapshot |null) =>void

    A callbackfunction that will be called when the transaction completes. The callbackis passed three arguments: a possibly-nullError, aboolean indicatingwhether the transaction was committed, and aDataSnapshot indicating thefinal result. If the transaction failed abnormally, the first argument willbe anError object indicating the failure cause. If the transactionfinished normally, but no data was committed because no data was returnedfromtransactionUpdate, then second argument will be false. If thetransaction completed and committed data to Firebase, the second argumentwill be true. Regardless, the third argument will be aDataSnapshotcontaining the resulting data in this location.

    • • (a:Error |null, b:boolean, c:DataSnapshot |null):void

      • Parameters

        • a:Error |null

        • b:boolean

        • c:DataSnapshot |null

        Returnsvoid

  • Optional applyLocally:boolean

    By default, events are raised each time thetransaction update function runs. So if it is run multiple times, you maysee intermediate states. You can set this to false to suppress theseintermediate states and instead wait until the transaction has completedbefore events are raised.

  ReturnsPromise<TransactionResult>

  Returns a Promise that can optionally be used instead of the onCompletecallback to handle success and failure.

update

• update(values: Object, onComplete?: (a: Error |null) =>void):Promise<void>

• Writes multiple values to the Database at once.

  Thevalues argument contains multiple property-value pairs that will bewritten to the Database together. Each child property can either be a simpleproperty (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 updateonly the referenced properties at the current location (instead of replacingall the child properties at the current location).

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

  A singleupdate() will generate a single "value" event at the locationwhere theupdate() was performed, regardless of how many children weremodified.

  Note that modifying data withupdate() will cancel any pendingtransactions 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.

  See Introducing multi-location updates and more.

  example

  var adaNameRef = firebase.database().ref('users/ada/name');// Modify the 'first' and 'last' properties, but leave other data at// adaNameRef unchanged.adaNameRef.update({first:'Ada',last:'Lovelace' });

  Parameters

  • values:Object

    Object containing multiple values.

  • Optional onComplete:(a:Error |null) =>void

    Callback called when write to server iscomplete.

    • • (a:Error |null):void

      • Parameters

        • a:Error |null

        Returnsvoid

  ReturnsPromise<void>

  Resolves when update on server is complete.