Using JQuery in Chrome user scripts

It's been a while since Chrome supports user scripts. Chrome's user scripts runtime works pretty similar to Firefox + Greasemonkey's, but it is still not (and may will never be) fully compatible to FF+GM's runtime.

While writing user scripts, you may find JQuery a very powerful tool. It is a javascript library with many handy functions for extracting and manipulating HTML code in runtime.

In order to use JQuery within a user script, you may either download JQuery and embed it (being Minified version particularly insteresting in this case), or you may add some code to load JQuery with the actual page being fetched. I like the last better since it keeps my scripts smaller and cleaner, and linked to the latest version of JQuery. Unfortunately, this piece of code if incompatible with Chrome user scripts API.

Here is the modified version which works in Chrome:

// ==UserScript==
// @match        http://*
// @run-at       document-start
// ==/UserScript==

var jq_script = document.createElement("script");
jq_script.src = "http://jquery.com/src/jquery-latest.js";
jq_script.type = "text/javascript";
document.getElementsByTagName("html")[0].appendChild(jq_script);

function wait_for_jquery(attempts) {
  try {
    $ = window.jQuery || this.jQuery;
  } catch(err) { alert(err); }
  if ($ == null || typeof $ == "undefined") {
    if (attempts > 0) {
      window.setTimeout(wait_for_jquery, 250, attempts-1);
    }
  } else { letsJQuery(); }
}
wait_for_jquery(20);

function letsJQuery() {
  alert($);
}

Core changes are:

Added instruction // @run-at document-start

Using "html" node rather than "head" in document.getElementsByTagName("html")[0].appendChild(jq_script);

Using window.JQuery rather than windowUnsafe.JQuery