runtime.Port
APort
object represents one end of a connection between two specific contexts, which can be used to exchange messages.
One side initiates the connection, using aconnect()
API. This returns aPort
object. The other side listens for connection attempts using anonConnect
listener. This is passed a correspondingPort
object.
Once both sides havePort
objects, they can exchange messages usingPort.postMessage()
andPort.onMessage
. When they are finished, either end can disconnect usingPort.disconnect()
, which will generate aPort.onDisconnect
event at the other end, enabling the other end to do any cleanup required.
APort
can also become disconnected in response to various events. SeeLifecycle.
You can use this pattern to communicate between:
- different parts of your extension (for example, betweencontent scripts andbackground scripts)
- between your extension and anative application running on the user's computer.
- between your extension and a different extension
You need to use different connection APIs for different sorts of connections, as detailed in the table below.
Connection type | Initiate connection attempt | Handle connection attempt |
---|---|---|
Background script to content script | tabs.connect() | runtime.onConnect |
Content script to background script | runtime.connect() | runtime.onConnect |
Extension to native application | runtime.connectNative() | Not applicable (seeNative messaging). |
Extension to Extension | runtime.connect() | runtime.onConnectExternal |
Type
Values of this type are objects. They contain the following properties:
name
string
. The port's name, defined in theruntime.connect()
ortabs.connect()
call that created it. If this port is connected to a native application, its name is the name of the native application.disconnect
function
. Disconnects a port. Either end can call this when they have finished with the port. It will causeonDisconnect
to be fired at the other end. This is useful if the other end is maintaining some state relating to this port, which can be cleaned up on disconnect. If this port is connected to a native application, this function will close the native application.error
object
. If the port was disconnected due to an error, this will be set to an object with a string propertymessage
, giving you more information about the error. SeeonDisconnect
.onDisconnect
object
. This contains theaddListener()
andremoveListener()
functions common to all events for extensions built using WebExtension APIs. Listener functions will be called when the other end has calledPort.disconnect()
. This event will only be fired once for each port. The listener function will be passed thePort
object. If the port was disconnected due to an error, then thePort
argument will contain anerror
property giving more information about the error:jsport.onDisconnect.addListener((p) => { if (p.error) { console.log(`Disconnected due to an error: ${p.error.message}`); }});
Note that in Google Chrome
port.error
is not supported: instead, useruntime.lastError
to get the error message.onMessage
object
. This contains theaddListener()
andremoveListener()
functions common to all events for extensions built using WebExtension APIs. Listener functions will be called when the other end has sent this port a message. The listener will be passed the value that the other end sent.postMessage
function
. Send a message to the other end. This takes one argument, which is a serializable value (seeData cloning algorithm) representing the message to send. It will be delivered to any script listening to the port'sonMessage
event, or to the native application if this port is connected to a native application.sender
Optionalruntime.MessageSender
. Contains information about the sender of the message. Only present on ports passed to theruntime.onConnect
,runtime.onConnectExternal
, orruntime.onUserScriptConnect
listeners.
Lifecycle
The lifecycle of aPort
is describedin the Chrome docs.
There is, however, one important difference between Firefox and Chrome, stemming from the fact that theruntime.connect
andtabs.connect
APIs are broadcast channels. This means that there may be potentially more than one recipient, and this results in ambiguity when one of the contexts with aruntime.onConnect
call is closed. In Chrome, a port stays active as long as there is any other recipient. In Firefox, the port closes when any of the contexts unloads. In other words, the disconnection condition,
- All frames that received the port (via
runtime.onConnect
) have unloaded.
which holds in Chrome, is replaced by
- Any frame that received the port (via
runtime.onConnect
) has unloaded.
in Firefox (seebug 1465514).
Examples
Connecting from content scripts
This content script:
- connects to the background script and stores the
Port
in a variable calledmyPort
. - listens for messages on
myPort
and logs them. - sends messages to the background script, using
myPort
, when the user clicks the document.
// content-script.jslet myPort = browser.runtime.connect({ name: "port-from-cs" });myPort.postMessage({ greeting: "hello from content script" });myPort.onMessage.addListener((m) => { console.log("In content script, received message from background script: "); console.log(m.greeting);});document.body.addEventListener("click", () => { myPort.postMessage({ greeting: "they clicked the page!" });});
The corresponding background script:
listens for connection attempts from the content script.
when it receives a connection attempt:
- stores the port in a variable named
portFromCS
. - sends the content script a message using the port.
- starts listening to messages received on the port, and logs them.
- stores the port in a variable named
sends messages to the content script, using
portFromCS
, when the user clicks the extension's browser action.
// background-script.jslet portFromCS;function connected(p) { portFromCS = p; portFromCS.postMessage({ greeting: "hi there content script!" }); portFromCS.onMessage.addListener((m) => { console.log("In background script, received message from content script"); console.log(m.greeting); });}browser.runtime.onConnect.addListener(connected);browser.browserAction.onClicked.addListener(() => { portFromCS.postMessage({ greeting: "they clicked the button!" });});
Multiple content scripts
If you have multiple content scripts communicating at the same time, you might want to store each connection in an array.
// background-script.jslet ports = [];function connected(p) { ports[p.sender.tab.id] = p; // …}browser.runtime.onConnect.addListener(connected);browser.browserAction.onClicked.addListener(() => { ports.forEach((p) => { p.postMessage({ greeting: "they clicked the button!" }); });});
Connecting to native applications
This example connects to the native application "ping_pong" and starts listening for messages from it. It also sends the native application a message when the user clicks a browser action icon:
/*On startup, connect to the "ping_pong" app.*/let port = browser.runtime.connectNative("ping_pong");/*Listen for messages from the app.*/port.onMessage.addListener((response) => { console.log(`Received: ${response}`);});/*On a click on the browser action, send the app a message.*/browser.browserAction.onClicked.addListener(() => { console.log("Sending: ping"); port.postMessage("ping");});
Browser compatibility
Note:This API is based on Chromium'schrome.runtime
API. This documentation is derived fromruntime.json
in the Chromium code.