Why Would a JavaScript Variable Start With a Dollar Sign

Why would a JavaScript variable start with a dollar sign?

Very common use in jQuery is to distinguish jQuery objects stored in variables from other variables.

For example, I would define:

var $email = $("#email"); // refers to the jQuery object representation of the dom object
var email_field = $("#email").get(0); // refers to the dom object itself

I find this to be very helpful in writing jQuery code and makes it easy to see jQuery objects which have a different set of properties.

What is the purpose of the dollar sign in JavaScript?

A '$' in a variable means nothing special to the interpreter, much like an underscore.

From what I've seen, many people using jQuery (which is what your example code looks like to me) tend to prefix variables that contain a jQuery object with a $ so that they are easily identified and not mixed up with, say, integers.

The dollar sign function $() in jQuery is a library function that is frequently used, so a short name is desirable.

Why use $ (dollar sign) in the name of javascript variables?

The $ in the variable name is only part of the name, but the convention is to use it to start variable names when the variable represents a jQuery object.

var $myHeaderDiv = $('#header');
var myHeaderDiv = document.getElementById('header');

Now later in your code, you know the $myHeaderDiv is already a jQuery object, so you can call jQuery functions:

$myHeaderDiv.fade();

To get from the DOM-variable to the jQuery variable:

var $myHeaderDiv = jQuery(myHeaderDiv); //assign to another variable
jQuery(myHeaderDiv).fade(); //use directly

//or, as the $ is aliased to the jQuery object if you don't specify otherwise:
var $myHeaderDiv = jQuery(myHeaderDiv); //assign
$(myHeaderDiv).fade(); //use

To get from the jQuery variable to the DOM-variable.

var myHeaderDiv = $myHeaderDiv.get(0);

What is a difference between JS variables - with and without dollar sign?

It just a developer taste. Suppose you want to save a HTML element in a variable in your program you do this.

var $input = $('input');

So when ever we see the variable $input we are sure that this hold a jQuery object (the html element on which jquery library functions can be performed on eg: $input.toggle(), $input.remove(), $input.val() etc).

where the normal variable name without $ are to point out program variables. For Example we can say variables which holds some values that cant perform math operations. like

var shippingCost = 40;
var quantity = $('#totalQuantity').val();
  var totalCost = $('#totalCost').val();
  var finalPrice = (totalCost * quantity )+ shippingCost;

So you see here we do more of a math operations.

Also the usage of $ in variable names is purely the developers interest it all bubbles up to the code readability. Its just one of the Jquery Beast Coding Practices.

What does $ sign at the end of function name indicate?

Syntactically, the dollar ($) character has no special meaning in JavaScript identifiers.

It is, however, sometimes used by convention to indicate that a variable holds an Observable or that a function will return an Observable.

What does ${} (dollar sign and curly braces) mean in a string in JavaScript?

You're talking about template literals.

They allow for both multiline strings and string interpolation.

Multiline strings:

console.log(`foo

bar`);

// foo

// bar

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 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.

Reading a javascript script, why so many $ (dollar signs)?

I think you are reading a JavaScript library famously known as jQuery (or possibly another library). The $ is just a short form for a namespace or use as an identifier.

You can think of it like this jQuery('p') to select all the paragraphs on a page,
or for short form you can just write $('p').

Here is a link for jQuery tutorials/docs jQuery

Here is a list of standards section 7.6 describes it in detail ECMA Standard

When/why to prefix variables with $ when using jQuery?

It's a common reference to a jQuery wrapped object. It makes reading the code easier to know which variables are jQuery wrapped.

//Item has been "cached" for later use in the script as a jQuery object.
var $item = $(this);

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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