runtime.onMessage

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.

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 (en-US) 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. This is a preferred way.

The listener function can return either a Boolean or a Promise.

警告： Do not call addListener using the async function, as in:

js

browser.runtime.onMessage.addListener(async (data, sender) => {
  if (data.type === 'handle_me') return 'done';
});

as the listener will consume every message it receives, effectively blocking all other listeners from receiving and processing messages.

If you want to take an asynchronous approach, use a promise instead, as in:

js

browser.runtime.onMessage.addListener(data, sender) => {
  if (data.type === 'handle_me') return Promise.resolve('done');
});

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 (en-US) 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) {
  var 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, that 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 bookmarks.search() (en-US) 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);

• beastify
• content-script-register
• cookie-bg-picker
• devtools-panels
• export-helpers
• find-across-tabs
• imagify
• mocha-client-tests
• notify-link-clicks-i18n
• store-collected-images
• user-script-register
• webpack-modules