Use this event to listen for messages from another part of your extension.
Some example use cases are:
To send a message that is received by the
onMessage()
listener, use
runtime.sendMessage()
or (to send a message to a content script)
tabs.sendMessage()
.
注意：
Avoid creating multiple
onMessage()
listeners for the same type of message, because the order in which multiple listeners will fire is not guaranteed.
If you want to guarantee the delivery of a message to a specific end point, use the connection-based approach to exchange messages .
Along with the message itself, the listener is passed:
sender
object giving details about the message sender.
sendResponse()
function that can be used 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:
true
from the event listener. This keeps the
sendResponse()
function valid after the listener returns, so you can call it later.
See an example
.
Promise
from the event listener, and resolve when you have the response (or reject it in case of an error).
See an example
.
注意： You can also use a connection-based approach to exchange messages .
browser.runtime.onMessage.addListener(listener)
browser.runtime.onMessage.removeListener(listener)
browser.runtime.onMessage.hasListener(listener)
Events have three functions:
addListener(listener)
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 at least one listener is registered for this event. Returns
true
if it is listening,
false
否则。
listener
A callback function that will be called when this event occurs. The function will be passed the following arguments:
message
对象
. The message itself. This is a serializable object (see
Data cloning algorithm
).
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 serializable object (see
Data cloning algorithm
). 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:
sendResponse()
argument and return
true
from the listener function. You will then be able to call
sendResponse()
after the listener function has returned.
Promise
from the listener function and resolve the promise when the response is ready. This is a preferred way.
listener
function can return either a Boolean or a
Promise
.
注意：
If you pass an async function to
addListener()
, the listener will return a Promise for every message it receives, preventing other listeners from responding:
// don't do this
browser.runtime.onMessage.addListener(
async (data, sender) => {
if (data.type === 'handle_me') { return 'done'; }
}
);
If you only want the listener to respond to messages of a certain type, you must define the listener as a non-
async
function, and return a Promise only for the messages the listener is meant to respond to — and otherwise return false or undefined:
browser.runtime.onMessage.addListener(
(data, sender) => {
if (data.type === 'handle_me') {
return Promise.resolve('done');
}
return false;
}
);
BCD tables only load in the browser
This content script listens for click events on 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
});
}
This content script sends a message to the background script when the user clicks on 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) {
const sending = browser.runtime.sendMessage({content: "message from the content script"});
sending.then(handleResponse, handleError);
}
window.addEventListener("click", sendMessage);
Here is a 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);
And here is another version which uses
Promise.resolve()
:
// background-script.js
function handleMessage(request, sender, sendResponse) {
console.log(`content script sent a message: ${request.content}`);
return Promise.resolve({response: "response from background script"});
}
browser.runtime.onMessage.addListener(handleMessage);
Here is 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);
This content script gets the first
<a>
link on 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 is the background script. It uses
to see if the link is bookmarked, which returns a
bookmarks.search()
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
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);
注意：
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.
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