runtime.onUserScriptMessage

browser.runtime.onUserScriptMessage.addListener(listener)
browser.runtime.onUserScriptMessage.removeListener(listener)
browser.runtime.onUserScriptMessage.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 a listener is registered for this event. Returns true if it is listening, false otherwise.

listener

The function called when this event occurs. The function is passed these arguments:

message

object. The message. 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 one argument, which is any JSON-ifiable object. This argument is passed back to the message sender.

If you have more than one onUserScriptMessage listener in the same document, then only one can send a response.

To send a response synchronously, call sendResponse before the listener function returns. To send a response asynchronously, do one of these:

• keep a reference to the sendResponse argument and return true from the listener function. You can then call sendResponse after the listener function has returned.
• return a Promise from the listener function and resolve the promise when the response is ready.

In this example, a user script in a USER_SCRIPT world with the ID myScriptWorld sends a message to the extension that registered it:

// The user script
// Send a message to the extension that registered the user script
browser.runtime.sendMessage("my message");

// The extension that registered the user script

function handleMessage(message, sender) {
  // check that the message originated from "myScriptWorld" world
  if (sender.userScriptWorldId === "myScriptWorld") {
    // process message
    console.log(message);
  }
}

browser.runtime.onUserScriptMessage.addListener(handleMessage);

• userScripts-mv3