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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:

You need to use different connection APIs for different sorts of connections, as detailed in the table below.

Connection typeInitiate connection attemptHandle connection attempt
Background script to content scripttabs.connect()runtime.onConnect
Content script to background scriptruntime.connect()runtime.onConnect
Extension to native applicationruntime.connectNative() Not applicable (seeNative messaging).
Extension to Extensionruntime.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:

js
port.onDisconnect.addListener((p) => {  if (p.error) {    console.log(`Disconnected due to an error: ${p.error.message}`);  }});

Note that in Google Chromeport.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.

senderOptional

runtime.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 (viaruntime.onConnect) have unloaded.

which holds in Chrome, is replaced by

  • Any frame that received the port (viaruntime.onConnect) has unloaded.

in Firefox (seebug 1465514).

Examples

Connecting from content scripts

This content script:

  • connects to the background script and stores thePort in a variable calledmyPort.
  • listens for messages onmyPort and logs them.
  • sends messages to the background script, usingmyPort, when the user clicks the document.
js
// 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 namedportFromCS.
    • sends the content script a message using the port.
    • starts listening to messages received on the port, and logs them.
  • sends messages to the content script, usingportFromCS, when the user clicks the extension's browser action.

js
// 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.

js
// 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:

js
/*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.

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