This extension demonstrates how to use export helpers in Firefox to share JavaScript objects defined in content scripts with scripts loaded by web pages.

How it works

This example is in two parts:

an extension that consists of a content script and a background script
a web page at: https://mdn.github.io/webextensions-examples/export-helpers.html

The extension

The extension loads a content script into the page at: https://mdn.github.io/webextensions-examples/export-helpers.html. The content script:

defines a function notify() and uses exportFunction() to export it to the page as a property of the global window object.
defines an object messenger, that has a member function notify(), and uses cloneInto() to export that to the page as a property of the global window object.

In the implementation of notify(), the content script sends a message to the extension's background script: when the background script gets the messages, it displays a notification.

The page

The page is just a normal web page. It contains two buttons and loads a script. The script:

listens for clicks on the first button and calls:

window.notify("Message from the page script!");
listens for clicks on the other button and calls:

window.messenger.notify("Message from the page script!");

These items are available in the page's scope because the content script exported them.

How to use it

To see the extension in action:

install the extension
visit https://mdn.github.io/webextensions-examples/export-helpers.html
click one of the buttons in the page. You should see a notification from the extension.