What Is the Meaning of Symbol $ in Jquery

What is the meaning of symbol $ in jQuery?

The jQuery object :)

From the jQuery documentation:

By default, jQuery uses "$" as a shortcut for "jQuery"

So, using $("#id") or jQuery("#id") is the same.

What does the $ sign mean in jQuery or JavaScript?

In JavaScript it has no special significance (no more than a or Q anyway). It is just an uninformative variable name.

In jQuery the variable is assigned a copy of the jQuery function. This function is heavily overloaded and means half a dozen different things depending on what arguments it is passed. In this particular example you are passing it a string that contains a selector, so the function means "Create a jQuery object containing the element with the id Text".

How the symbol $ in jquery works?

The jQuery JavaScript file has the following line in it:

window.jQuery = window.$ = jQuery;

Meaning that the window-scoped $ variable will be assigned to the jQuery namespace, in which all the jQuery functions are placed under. This is why you can use jQuery in your code as well as $.

You could do this easily yourself by the same method and another character symbol, even:

window.$$ = jQuery;

would mean that jQuery is now assigned to $$, etc.

Does the '@' symbol have special meaning in Javascript, Coffeescript or Jquery?

@ is not a valid character for a javascript identifier. Identifiers may only contain $, _, digits and letters.

In coffeescript, @ means this.

CoffeeScript has a few nice features related to the this keyword.
First, CoffeeScript uses the @ symbol as shorthand for this.. For
example, @foo is equivalent to this.foo. Second, if you use the @
symbol in the parameters of a function, CoffeeScript will
automatically assign those values as properties of the object.

Edit: As far as jQuery is concerned, the same identifier rules as javascript apply since jQuery is just javascript. For other uses of @ in jQuery, see this question or the docs.

What do dot and hash symbols mean in JQuery?

The hash (#) specifies to select elements by their ID's

The dot (.) specifies to select elements by their classname

You can read more about the selectors here: http://api.jquery.com/category/selectors/basic-css-selectors/

What is the meaning of $ sign in JavaScript

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-case letters (in a wide variety of scripts, not just English), numbers (but not at the first character), $, _, and others.¹

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.

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¹ For the first character of an identifier, JavaScript allows "...any Unicode code point with the Unicode property “ID_Start”..." plus $ and _; details in the specification. For subsequent characters in an identifier, it allows anything with ID_Continue (which includes _) and $ (and a couple of control characters for historical compatibility).

Why does JQuery have dollar signs everywhere?

$ is just a shortcut for jQuery. The idea is that everything is done with the one global symbol (since the global namespaces is ridiculously crowded), jQuery, but you can use $ (because it's shorter) if you like:

// These are the same barring your using noConflict (more below)
var divs = $("div");       // Find all divs
var divs = jQuery("div");  // Also find all divs, because
console.log($ === jQuery); // "true"

If you don't want to use the alias, you don't have to. And if you want $ to not be an alias for jQuery, you can use noConflict and the library will restore $ to whatever it was before jQuery took it over. (Useful if you also use Prototype or MooTools.)

What is the $ symbol used for in JavaScript

It doesn't mean anything special.

But because $ is allowed in identifier names, many Javascript libraries have taken to using $ as the "central" interface to them, or at least as a shortcut for accessing their functionality.

For example, if you're using jQuery and you say $("div"), this is a call to the $ function with argument "div". When you say $.post(), it's calling the post method on the $ object (Javascript is nice in that functions are first-class objects).

What does the '#' sign mean in jQuery?

In JavaScript? Nothing special. It is just part of a string.

The $ function might do something with it, but it is hard to tell what the $ function is.

There are a lot of libraries which provide a $ function that acts as a kitchen sink for that library. They include Prototype, Mootools and jQuery. This one looks most like jQuery, in which case the argument is a string containing a CSS selector, so the # indicates the start of an id selector.

This "Selects a single element with the given id attribute".

What's the meaning of $ in front of a variable

As everyone said, its just a convention.

I use the $ sign in front of a variable to identify that this variable holds an object.

var thisIsANumber = 1024; // No $.. Its a normal variable
var $divElement = $('div#idOfDiv'); // Yes! Its a jQuery Object
var $this = $(this); // Commonly used to reduce the work javascript has to do!

//Now I can use something like this.. (Notice how easy it is to read!)
$divElement.slideUp();

// Or a more `real world` example!
$('#element').click(function(){
    // Hold $(this) inside a variable
    // So we don't have to traverse the dom unnecessarily
    var $this = $(this); // Save it (its a object.. so prepend a `$` )
    $this.hide(); // Use it again
    $this.fadeIn(); // and again
//  ^ Has a dollar sign, because it is a jQuery Object.
});

You will see loads of plugins use this convention (well.. at least the well written ones).

By storing the object inside a variable, Javascript doesn't have to crawl through your code each time to get the element. Instead, we already have the element (inside the variable), so we use that to reference it.

If you use $(this) more then once inside the same callback function, you should store it inside a variable.. (var $this = $(this);). Otherwise, every time you use it, javascript will have to get the element from your source code each time (which can massively decrease performance! (especially for people browsing on a slow/old computer!).

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