What is the meaning of "$" sign in JavaScript

Question

In the following JavaScript code there is a dollar ($) sign. What does it mean?

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

Answer 1

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 2

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 a 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!

When Prototype library arrived, they named their function, which gets the DOM elements, as '$'. Almost all the JavaScript libraries copied this idea. Prototype also introduced a $$ function to select elements using CSS selector.

jQuery also adapted $ function but expanded to make it accept all kinds 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! :)

Answer 3

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 4

As all the other answers say; it can be almost anything but is usually "JQuery".

However, in ES6 it is a string interpolation operator in a template "literal" eg.

var s = "new" ; // you can put whatever you think appropriate here.
var s2 = `There are so many ${s} ideas these days !!` ; //back-ticks not quotes
console.log(s2) ;

result:

There are so many new ideas these days !!

Answer 5

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

Answer 6

In addition to the above answers, $ has no special meaning in javascript,it is free to be used in object naming. In jQuery, it is simply used as an alias for the jQuery object and jQuery() function. However, you may encounter situations where you want to use it in conjunction with another JS library that also uses $, which would result a naming conflict. There is a method in JQuery just for this reason, jQuery.noConflict().

Here is a sample from jQuery doc's:

<script src="other_lib.js"></script>
<script src="jquery.js"></script>
<script>
$.noConflict();
// Code that uses other library's $ can follow here.
</script>

Alternatively, you can also use a like this

(function ($) {
// Code in which we know exactly what the meaning of $ is
} (jQuery));

Ref:https://api.jquery.com/jquery.noconflict/

Answer 7

From the jQuery documentation describing the jQuery Core Object:

Many developers prefix a $ to the name of variables that contain jQuery objects in order to help differentiate. There is nothing magic about this practice – it just helps some people keep track of what different variables contain.

Answer 8

Basic syntax is: $(selector).action()

A dollar sign to define jQuery A (selector) to "query (or find)" HTML elements A jQuery action() to be performed on the element(s)