runtime.onUserScriptMessage

Syntax

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.

addListener syntax

Parameters

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.

Examples

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);

Example extensions

• userScripts-mv3

Browser compatibility