A Port
object represents one end of a connection between two specific contexts, which can be used to exchange messages.
One side initiates the connection, using a connect()
API. This returns a Port
object. The other side listens for connection attempts using an onConnect
listener. This is passed a corresponding Port
object.
Once both sides have Port
objects, they can exchange JSON messages using Port.postMessage()
and Port.onMessage
. When they are finished, either end can disconnect using Port.disconnect()
, which will generate a Port.onDisconnect
event at the other end, enabling the other end to do any cleanup required.
You can use this pattern to communicate between:
- different parts of your extension (for example, between content scripts and background scripts)
- between your extension and a native 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 (see Native 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:port.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 JSON object that the other end sent.postMessage
function
. Send a message to the other end. This takes one argument, which is a JSON object 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. This property will only be present on ports passed toonConnect
/onConnectExternal
listeners.
Browser compatibility
The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Chrome | Edge | Firefox | Firefox for Android | Opera | |
---|---|---|---|---|---|
Basic support | 26 | 15 | 45 | 48 | 15 |
error | No | No | 52 | 52 | No |
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.js
var myPort = browser.runtime.connect({name:"port-from-cs"});
myPort.postMessage({greeting: "hello from content script"});
myPort.onMessage.addListener(function(m) {
console.log("In content script, received message from background script: ");
console.log(m.greeting);
});
document.body.addEventListener("click", function() {
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.js
var portFromCS;
function connected(p) {
portFromCS = p;
portFromCS.postMessage({greeting: "hi there content script!"});
portFromCS.onMessage.addListener(function(m) {
console.log("In background script, received message from content script")
console.log(m.greeting);
});
}
browser.runtime.onConnect.addListener(connected);
browser.browserAction.onClicked.addListener(function() {
portFromCS.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. */ var 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"); });
This API is based on Chromium's chrome.runtime
API. This documentation is derived from runtime.json
in the Chromium code.
Microsoft Edge compatibility data is supplied by Microsoft Corporation and is included here under the Creative Commons Attribution 3.0 United States License.
// Copyright 2015 The Chromium Authors. All rights reserved. // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are // met: // // * Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // * Redistributions in binary form must reproduce the above // copyright notice, this list of conditions and the following disclaimer // in the documentation and/or other materials provided with the // distribution. // * Neither the name of Google Inc. nor the names of its // contributors may be used to endorse or promote products derived from // this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.