Use this event to listen for messages from another part of your add-on. For example, you can use it:
  • 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.



Events have three functions:

Adds a listener to this event.
Stop listening to this event. The listener argument is the listener to remove.
Checks whether a listener is registered for this event. Returns true if it is listening, false otherwise.

addListener syntax



A listener function that will be called when this event occurs. The function will be passed the following arguments:

object. The message itself. This is a JSON-ifiable object.
A runtime.MessageSender object representing the sender of the message.

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, keep a reference to the sendResponse argument and return true from the listener function. You will then be able to call sendResponse after the listener function has returned.

The listener function returns a boolean. It should return true if you wish to call sendResponse after the listener returns.

Browser compatibility

Chrome Edge Firefox Firefox for Android Opera
Basic support Yes Yes 45.0 48.0 33

Compatibility notes


  • 'MessageSender.tlsChannelId' is not supported.


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 ( != "A") {

The background script listens for these messages and displays a notification using the notifications API:

// background-script.js


function notify(message) {
    "type": "basic",
    "iconUrl": browser.extension.getURL("link.png"),
    "title": "You clicked a link!",
    "message": message.url

Sending a 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"});


Here's an alternative version of the background script, that 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;


Example add-ons


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.

Document Tags and Contributors

 Contributors to this page: wbamberg, Makyen, chrisdavidmills
 Last updated by: wbamberg,