what is the meaning of "$" sign in javascript

Question

In the flowing javascript code there is one $(window). What does it mean???

$(window).bind('load', function() {
$('img.protect').protectImage();
});

Answer 1

That is most likely jQuery code (more precisely, JavaScript using the jQuery library).

The $ represents the jQuery Function, and is actually a shorthand alias for jQuery. (Unlike in most languages, the $ symbol is not reserved, and may be used as a variable name.) It is typically used as a selector (i.e. a function that returns a set of elements found in the DOM).

Answer 2

Probably JQuery.

link text

Answer 3

the "$()" is the shorthand version of jQuery() used in jQuery Library

Answer 4

Your snippet of code looks like it's referencing methods from one of the popular JavaScript libraries (jQuery, ProtoType, mooTools, and so on).

There's nothing mysterious about the use of "$" in JavaScript. $ is simply a valid JavaScript identifier.

JavaScript allows upper and lower letters, numbers, and $ and _. The $ was intended to be used for machine-generated variables (such as $0001).

Prototype, jQuery, and most javascript libraries use the $ as the primary base object (or function). Most of them also have a way to relinquish the $ so that it can be used with another library that uses it. In that case you use "jQuery" instead of "$". In fact, "$" is just a shortcut for "jQuery".

Answer 5

From another answer:

A little history

Remember, there is nothing inherently special about '$'. It is a variable name just like any other. In earlier days, people used to write code using document.getElementById. Because JavaScript is case-sensitive, it was normal to make mistake while writing document.getElementById. Should I capital 'b' of 'by'? Should I capital 'i' of Id? You get the drift. Because functions are first class citizens in JavaScript, you can always do this

var $ = document.getElementById; //freedom from document.getElementById!

[EDIT: Looks like in Firefox 3 and Google Chrome, you can't make alias so easily. In IE6 and Firefox2, above technique still works.]

When Prototype library arrived, they named their function, which gets the DOM elements, as '$' to save on typing/readability [When writing JS code, most of the time you start with selecting some DOM elements]. Almost all the JavaScript libraries copied this idea. Prototype also introduced $$ function to select elements using CSS selector.

jQuery not only adapted the '$ function', but expanded to make it accept all kind of 'selectors' to get the elements you want. Now, if you are already using Prototype in your project and wanted to include jQuery, you will be in problem as '$' could either refer to Prototype's implementation OR jQuery's implementation. That's why jQuery has the option of noConflict so that you can include jQuery in your project which uses Prototype and slowly migrate your code. I think this was a brilliant move on John's part! :)