- in a content script, to listen for messages from a background script
- in a background script, to listen for messages from a content script
- in an options page or popup script, to listen for messages from a background script
- in an background script, to listen for messages from a options page or popup script.
To send a message which will be received by the onMessage
listener, use runtime.sendMessage()
or (to send a message to a content script) tabs.sendMessage()
.
Along with the message itself, the listener is passed:
- a
sender
object giving details about the message sender - a
sendResponse
function which it can use to send a response back to the sender.
You can send a synchronous response to the message by calling the sendResponse
function inside your listener. See an example.
To send an asynchronous response, there are two options:
- return
true
from the event listener. This keeps thesendResponse
function valid after the listener returns, so you can call it later. See an example. - return a
Promise
from the event listener, and resolve when you have the response (or reject it in case of an error). See an example.
In Firefox versions prior to version 51, the runtime.onMessage
listener will be called for messages sent from the same script (e.g. messages sent by the background script will also be received by the background script). In those versions of Firefox, if you unconditionally call runtime.sendMessage() from within a runtime.onMessage
listener, you will set up an infinite loop which will max-out the CPU and lock-up Firefox. If you need to call runtime.sendMessage() from within a runtime.onMessage
, you will need to check the sender.url
property to verify you are not sending a message in response to a message which was sent from the same script. This bug was resolved as of Firefox 51.
Syntax
browser.runtime.onMessage.addListener(listener) browser.runtime.onMessage.removeListener(listener) browser.runtime.onMessage.hasListener(listener)
Events have three functions:
addListener(callback)
- Adds a listener to this event.
removeListener(listener)
- Stop listening to this event. The
listener
argument is the listener to remove. hasListener(listener)
- Checks whether a
listener
is registered for this event. Returnstrue
if it is listening,false
otherwise.
addListener syntax
Parameters
function
-
A listener function that will be called when this event occurs. The function will be passed the following arguments:
message
object
. The message itself. This is a JSON-ifiable object.
sender
- A
runtime.MessageSender
object representing the sender of the message.
sendResponse
-
A function to call, at most once, to send a response to the message. The function takes a single argument, which may be any JSON-ifiable object. This argument is passed back to the message sender.
If you have more than one
onMessage
listener in the same document, then only one may send a response.To send a response synchronously, call
sendResponse
before the listener function returns. To send a response asynchronously:- either keep a reference to the
sendResponse
argument and returntrue
from the listener function. You will then be able to callsendResponse
after the listener function has returned. - or return a
Promise
from the listener function and resolve the promise when the response is ready.
- either keep a reference to the
The listener function can return either a Boolean or a
Promise
.
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 | Yes | 45 | 48 | 15 |
Examples
Simple example
This content script listens for click events in the web page. If the click was on a link, it messages the background page with the target URL:
// content-script.js
window.addEventListener("click", notifyExtension);
function notifyExtension(e) {
if (e.target.tagName != "A") {
return;
}
browser.runtime.sendMessage({"url": e.target.href});
}
The background script listens for these messages and displays a notification using the notifications
API:
// background-script.js
browser.runtime.onMessage.addListener(notify);
function notify(message) {
browser.notifications.create({
"type": "basic",
"iconUrl": browser.extension.getURL("link.png"),
"title": "You clicked a link!",
"message": message.url
});
}
Sending a synchronous response
This content script sends a message to the background script when the user clicks in the page. It also logs any response sent by the background script:
// content-script.js function handleResponse(message) { console.log(`background script sent a response: ${message.response}`); } function handleError(error) { console.log(`Error: ${error}`); } function sendMessage(e) { var sending = browser.runtime.sendMessage({content: "message from the content script"}); sending.then(handleResponse, handleError); } window.addEventListener("click", sendMessage);
Here's one version of the corresponding background script, that sends a response synchronously, from inside in the listener:
// background-script.js function handleMessage(request, sender, sendResponse) { console.log(`content script sent a message: ${request.content}`); sendResponse({response: "response from background script"}); } browser.runtime.onMessage.addListener(handleMessage);
Sending an asynchronous response using sendResponse
Here's an alternative version of the background script from the previous example. It sends a response asynchronously, after the listener has returned. Note return true;
in the listener: this tells the browser that you intend to use the sendResponse
argument after the listener has returned.
// background-script.js function handleMessage(request, sender, sendResponse) { console.log(`content script sent a message: ${request.content}`); setTimeout(() => { sendResponse({response: "async response from background script"}); }, 1000); return true; } browser.runtime.onMessage.addListener(handleMessage);
Sending an asynchronous response using a Promise
Here's a content script that gets the first <a> link in the page, and sends a message asking if the link's location is bookmarked. It expects to get a Boolean response: true
if the location is bookmarked, false
otherwise:
// content-script.js const firstLink = document.querySelector("a"); function handleResponse(isBookmarked) { if (isBookmarked) { firstLink.classList.add("bookmarked"); } } browser.runtime.sendMessage({ url: firstLink.href }).then(handleResponse);
Here's the background script. It uses bookmarks.search()
to see if the link is bookmarked, which returns a Promise
:
// background-script.js function isBookmarked(message, sender, response) { return browser.bookmarks.search({ url: message.url }).then(function(results) { return results.length > 0; }); } browser.runtime.onMessage.addListener(isBookmarked);
If the asynchronous handler doesn't return a promise, you can explicitly construct a promise. This rather contrived example sends a response after a 1 second delay, using Window.setTimeout()
:
// background-script.js function handleMessage(request, sender, sendResponse) { return new Promise(resolve => { setTimeout(() => { resolve({response: "async response from background script"}); }, 1000); }); } browser.runtime.onMessage.addListener(handleMessage);
Example extensions
- beastify
- cookie-bg-picker
- embedded-webextension-bootstrapped
- embedded-webextension-sdk
- imagify
- notify-link-clicks-i18n
- proxy-blocker
- webpack-modules
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.