Hijacking a variable with a userscript for Chrome

Question

I\'m trying to change the variable in a page using a userscript. I know that in the source code there is a variable

var smilies = false;

I

Answer 1

In Content scripts (Chrome extensions), there's a strict separation between the page's global window object, and the content script's global object.

• To inject the code, a script tag has to be injected.
• Overwriting a variable is straightforward.
  Overwriting a variable, with the intention of preventing the variable from being overwritten requires the use of Object.defineProperty ^{Example + notes}.

The final Content script's code:

// This function is going to be stringified, and injected in the page
var code = function() {
    // window is identical to the page's window, since this script is injected
    Object.defineProperty(window, 'smilies', {
        value: true
    });
    // Or simply: window.smilies = true;
};
var script = document.createElement('script');
script.textContent = '(' + code + ')()';
(document.head||document.documentElement).appendChild(script);
script.parentNode.removeChild(script);