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Add-ons
  1. MDN
  2. Mozilla
  3. Add-ons
  4. Browser extensions
  5. JavaScript APIs
  6. runtime
  7. runtime.onMessage

runtime.onMessage

In This Article
  1. Syntax
  2. addListener syntax
    1. Parameters
  3. Browser compatibility
  4. Examples
    1. Simple example
    2. Sending a synchronous response
    3. Sending an asynchronous response using sendResponse
    4. Sending an asynchronous response using a Promise
    5. Example extensions
Use this event to listen for messages from another part of your extension. 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.

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 the sendResponse 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. Returns true 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 return true from the listener function. You will then be able to call sendResponse after the listener function has returned.
  • or return a Promise from the listener function and resolve the promise when the response is ready.

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.

ChromeEdgeFirefoxFirefox for AndroidOpera
Basic support26Yes454815

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

Acknowledgements

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.

Document Tags and Contributors

Tags: 
  • Add-ons
  • API
  • Event
  • Extensions
  • Non-standard
  • onmessage
  • Reference
  • runtime
  • WebExtensions
 Contributors to this page: andrewtruongmoz, wbamberg, lemnis, Makyen, chrisdavidmills
 Last updated by: andrewtruongmoz, Jul 13, 2017, 2:51:17 PM
See also
  1. Browser extensions
  2. Getting started
    1. What are extensions?
    2. Your first extension
    3. Your second extension
    4. Anatomy of an extension
    5. Example extensions
  3. How to
    1. Intercept HTTP requests
    2. Modify a web page
    3. Add a button to the toolbar
    4. Implement a settings page
  4. User interface
    1. Introduction
    2. Toolbar button
    3. Address bar button
    4. Sidebar
    5. Context menu items
    6. Options page
    7. Bundled web pages
    8. Notifications
    9. Address bar suggestions
    10. Developer tools panels
  5. Concepts
    1. Using the JavaScript APIs
    2. Content scripts
    3. Match patterns
    4. Internationalization
    5. Content Security Policy
    6. Native messaging
  6. Porting
    1. Porting a Google Chrome extension
    2. Porting a legacy Firefox extension
    3. Embedded WebExtensions
    4. Comparison with the Add-on SDK
    5. Comparison with XUL/XPCOM extensions
    6. Chrome incompatibilities
    7. Differences between desktop and Android
  7. Firefox workflow
    1. Temporary Installation in Firefox
    2. Debugging
    3. Developing for Firefox for Android
    4. Getting started with web-ext
    5. web-ext command reference
    6. Extensions and the Add-on ID
    7. Publishing your extension
  8. JavaScript APIs
    1. Browser support for JavaScript APIs
    2. alarms
    3. bookmarks
    4. browserAction
    5. browsingData
    6. commands
    7. contextMenus
    8. contextualIdentities
    9. cookies
    10. devtools.inspectedWindow
    11. devtools.network
    12. devtools.panels
    13. downloads
    14. events
    15. extension
    16. extensionTypes
    17. history
    18. i18n
    19. identity
    20. idle
    21. management
    22. notifications
    23. omnibox
    24. pageAction
    25. permissions
    26. privacy
    27. proxy
    28. runtime
      1. Methods
        1. connect()
        2. connectNative()
        3. getBackgroundPage()
        4. getManifest()
        5. getPackageDirectoryEntry()
        6. getPlatformInfo()
        7. getURL()
        8. openOptionsPage()
        9. reload()
        10. requestUpdateCheck()
        11. sendMessage()
        12. sendNativeMessage()
        13. setUninstallURL()
      2. Properties
        1. id
        2. lastError
      3. Types
        1. MessageSender
        2. OnInstalledReason
        3. OnRestartRequiredReason
        4. PlatformArch
        5. PlatformInfo
        6. PlatformNaclArch
        7. PlatformOs
        8. Port
        9. RequestUpdateCheckStatus
      4. Events
        1. onBrowserUpdateAvailable
        2. onConnect
        3. onConnectExternal
        4. onInstalled
        5. onMessage
        6. onMessageExternal
        7. onRestartRequired
        8. onStartup
        9. onSuspend
        10. onSuspendCanceled
        11. onUpdateAvailable
    29. sessions
    30. sidebarAction
    31. storage
    32. tabs
    33. topSites
    34. types
    35. webNavigation
    36. webRequest
    37. windows
  9. Manifest keys
    1. applications
    2. author
    3. background
    4. browser_action
    5. chrome_settings_overrides
    6. chrome_url_overrides
    7. commands
    8. content_scripts
    9. content_security_policy
    10. default_locale
    11. description
    12. developer
    13. devtools_page
    14. homepage_url
    15. icons
    16. incognito
    17. manifest_version
    18. name
    19. omnibox
    20. optional_permissions
    21. options_ui
    22. page_action
    23. permissions
    24. protocol_handlers
    25. short_name
    26. sidebar_action
    27. version
    28. web_accessible_resources
  10. Themes
  11. Publishing add-ons
  12. Guides
    1. Signing and distribution overview
    2. Submit an add-on
    3. Creating an appealing listing
    4. Review policies
    5. Developer agreement
    6. Featured add-ons
    7. Contact addons.mozilla.org
  13. Community and support
  14. Channels
    1. Add-ons blog
    2. Add-on forums
    3. Stack Overflow
    4. Development newsgroup
    5. IRC Channel
  15. Legacy add-ons
  16. Legacy technologies
    1. Add-on SDK
    2. Legacy Firefox for Android
    3. Bootstrapped extensions
    4. Overlay extensions