Can the window object be modified from a Chrome extension?

Question

I would like to make a Chrome extension that provides a new object inside window. When a web page is viewed in a browser with the extension loaded, I would like

Answer 1

As others have pointed out, context scripts do not run in the same context as the page's, so, to access the correct window, you need to inject code into the page.

Here's my take at it:

function codeToInject() {
    // Do here whatever your script requires. For example:
    window.foo = "bar";
}

function embed(fn) {
    const script = document.createElement("script");
    script.text = `(${fn.toString()})();`;
    document.documentElement.appendChild(script);
}

embed(codeToInject);

Clean and easy to use. Whatever you need to run in the page's context, put it in codeToInject() (you may call it whatever you prefer). The embed() function takes care of packaging your function and sending it to run in the page.

What the embed() function does is to create a script tag in the page and embed the function codeToInject() into it as an IIFE. The browser will immediately execute the new script tag as soon as it's appended to the document and your injected code will run in the context of the page, as intended.