Add jQuery to your Greasemonkey script

Greasemonkey is a Firefox add-on that lets you run JavaScript on web pages you specify. Using Greasemonkey you can improve and change the way websites look and behave (see examples of what is possible here). To learn more about it see it's official site, to learn how to include and write your own custom scripts (aka "user scripts") visit coder's manual.

Usually Greasemonkey scripts work with the DOM and jQuery is the best way to do that. So, no wonder you'll want to include jQuery into your custom scripts. Here are 3 ways to include jQuery library into your user script.

If you are targeting for Greasemonkey 0.8.0+ you can use @require. It runs once when the script is being installed, hence downloaded once. This is preferred and most efficient way to add jQuery.

// ==UserScript==
// @name     My jQuery Test
// @require
// ==/UserScript==

// Do your magic here
If you are developing for older versions of Greasemonkey you have 2 options. Either add the whole jQuery library code into your Greasemonkey script file or dynamically add a <script> tag to the page.

Adding jQuery library right in your custom script

// ==UserScript==
// @name     My jQuery Test
// ==/UserScript==

// include jQuery library
 * jQuery JavaScript Library v1.6.2
 * Copyright 2011, John Resig
 * Dual licensed under the MIT or GPL Version 2 licenses.
 * Includes Sizzle.js
 * Copyright 2011, The Dojo Foundation
 * Released under the MIT, BSD, and GPL Licenses.
 * Date: Thu Jun 30 14:16:56 2011 -0400
(function(a,b){function cv(a){return f.isWindow(a)? ...

One more method to add jQuery

One more way to add jQuery is by attaching <script> tag to the document. You can read more about it and grab the code here.

Don't forget to check if jQuery is already loaded

if (unsafeWindow.jQuery === undefined) {
  // jQuery is NOT loaded
} else {
  // jQuery is already loaded

HTML: The difference between attribute and property

In this short post I will explain the difference between attributes and properties in HTML. The .prop() function introduced in jQuery 1.6 raised a lot of questions about the difference and I hope this post will help you to understand it.

What is an attribute?

Attributes carry additional information about an HTML element and come in name=”value” pairs. Example: <div class=”my-class”></div>. Here we have a div tag and it has a class attribute with a value of my-class.

What is a property?

Property is a representation of an attribute in the HTML DOM tree. So the attribute in the example above would have a property named className with a value of my-class.

Our DIV node
 |- nodeName = "DIV"
 |- className = "my-class"
 |- style
   |- ...
 |- ...

What is the difference between attribute and property?

Attributes are in your HTML text document/file, whereas properties are in HTML DOM tree. This means that attributes do not change and always carry initial (default) values. However, HTML properties can change, for example when user checks a checkbox, inputs text to textarea or uses JavaScript to change the property value.

Here is a visual representation:
HTML                          DOM
<input value="default" />     value = default

Current values:
Attribute: "default"          Property:  "default"

Assume user inputs his name "Joe" into the inputbox. Here are what attribute and property values of an element will be.

HTML                          DOM
<input value="default" />     value = Joe

Current values:
Attribute: "default"          Property:  "Joe"

As you can see, only element’s property is changed, because it is in the DOM and dynamic. But element’s attribute is in HTML text and can not be changed!

I hope this helps to understand the difference between attributes and properties. If you have any questions please leave them on jQueryHowto Facebook page.

Also, stay tuned for the next post about the difference between jQuery.attr() and jQuery.prop() and when to use one over another.