You can do something like this:

var theWindow = window.open('http://stackoverflow.com'),

    theDoc = theWindow.document,

    theScript = document.createElement('script');

function injectThis() {

    // The code you want to inject goes here

    alert(document.body.innerHTML);

}

theScript.innerHTML = 'window.onload = ' + injectThis.toString() + ';';

theDoc.body.appendChild(theScript);

This also seems to work:

var theWindow = window.open('http://stackoverflow.com'),

    theScript = document.createElement('script');

function injectThis() {

    // The code you want to inject goes here

    alert(document.body.innerHTML);

}

// Self executing function

theScript.innerHTML = '(' + injectThis.toString() + '());';

theWindow.onload = function () {

    // Append the script to the new window's body.

    // Only seems to work with `this`

    this.document.body.appendChild(theScript);

};

And if for some reason you want to use eval:

var theWindow = window.open('http://stackoverflow.com'),

    theScript;

function injectThis() {

    // The code you want to inject goes here

    alert(document.body.innerHTML);

}

// Self executing function

theScript = '(' + injectThis.toString() + '());';

theWindow.onload = function () {

    this.eval(theScript);

};

What this does (Explanation for the first bit of code. All examples are quite similar):

• Opens the new window


• Gets a reference to the new window's document


• Creates a script element


• Places all the code you want to 'inject' into a function


• Changes the script's innerHTML to load said function when the window
  loads, with the window.onload event (you can also use addEventListener). I used toString() for convenience, so you don't have to concatenate a bunch of strings. toString basically returns the whole injectThis function as a string.


• Appends the script to the new window's document.body, it won't actually append it to the document that is loaded, it appends it before it loads (to an empty body), and that's why you have to use window.onload, so that your script can manipulate the new document.

It's probably a good idea to use window.addEventListener('load', injectThis.toString()); instead of window.onload, in case you already have a script within your new page that uses the window.onload event (it'd overwrite the injection script).

Note that you can do anything inside of the injectThis function: append DIVs, do DOM queries, add even more scripts, etc...

Also note that you can manipulate the new window's DOM inside of the theWindow.onload event, using this.