runtime.sendMessage()

Sends a single message to event listeners within your extension or a different extension.

If sending to your extension, omit theextensionId argument. The runtime.onMessage event will be fired in each page in your extension, except for the frame that calledruntime.sendMessage.

If sending to a different extension, include theextensionId argument set to the other extension's ID.runtime.onMessageExternal will be fired in the other extension. By default, your extension can exchange messages with itself and any other extension (defined byextensionId). However, theexternally_connectable manifest key can be used to limit communication to specific extensions.

Extensions cannot send messages to content scripts using this method. To send messages to content scripts, usetabs.sendMessage.

This is an asynchronous function that returns aPromise.

Note:You can also use aconnection-based approach to exchange messages.

Syntax

let sending = browser.runtime.sendMessage(  extensionId,             // optional string  message,                 // any  options                  // optional object)

Parameters

extensionIdOptional

string. The ID of the extension to send the message to. Include this to send the message to a different extension. If the intended recipient has set an ID explicitly using thebrowser_specific_settings key in manifest.json, thenextensionId should have that value. Otherwise it should have the ID that was generated for the intended recipient.

IfextensionId is omitted, the message is sent to your extension.

message

any. An object that can be structured clone serialized (seeData cloning algorithm).

optionsOptional

object.

includeTlsChannelIdOptional

boolean. Whether the TLS channel ID will be passed intoruntime.onMessageExternal for processes that are listening for the connection event.

This option is only supported in Chromium-based browsers.

Depending on the arguments it is given, this API is sometimes ambiguous. The following rules are used:

if one argument is given, it is the message to send, and the message will be sent internally.
if two arguments are given:
- the arguments are interpreted as(message, options), and the message is sent internally, if the second argument is any of the following:
  1. a validoptions object (meaning, it is an object which contains only the properties ofoptions that the browser supports)
  2. null
  3. undefined
- otherwise, the arguments are interpreted as(extensionId, message). The message will be sent to the extension identified byextensionId.
if three arguments are given, the arguments are interpreted as(extensionId, message, options). The message will be sent to the extension identified byextensionId.

Note that before Firefox 55, the rules were different in the 2-argument case. Under the old rules, if the first argument was a string, it was treated as theextensionId, with the message as the second argument. This meant that if you calledsendMessage() with arguments like("my-message", {}), then it would send an empty message to the extension identified by "my-message". Under the new rules, with these arguments you would send the message "my-message" internally, with an empty options object.

Return value

APromise. If the receiver sent a response, this will be fulfilled with the response. Otherwise it will be fulfilled with no arguments. If an error occurs while connecting to the extension, the promise will be rejected with an error message.

Examples

Here's a content script that sends a message to the background script when the user clicks the content window. The message payload is{greeting: "Greeting from the content script"}, and the sender also expects to get a response, which is handled in thehandleResponse function:

// content-script.jsfunction handleResponse(message) {  console.log(`Message from the background script: ${message.response}`);}function handleError(error) {  console.log(`Error: ${error}`);}function notifyBackgroundPage(e) {  const sending = browser.runtime.sendMessage({    greeting: "Greeting from the content script",  });  sending.then(handleResponse, handleError);}window.addEventListener("click", notifyBackgroundPage);

The corresponding background script looks like this:

// background-script.jsfunction handleMessage(request, sender, sendResponse) {  console.log(`A content script sent a message: ${request.greeting}`);  sendResponse({ response: "Response from background script" });}browser.runtime.onMessage.addListener(handleMessage);

Note:Instead of usingsendResponse(), returning aPromise is the recommended approach for Firefox add-ons.Examples using a Promise are available in theexamples section of theruntime.onMessage listener.