What Is the Meaning of "$" Sign in JavaScript

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.

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.

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 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".

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(`foobar`);// foo// bar

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.

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 does this symbol mean in JavaScript?

See the documentation on MDN about expressions and operators and statements.

Basic keywords and general expressions

`this` keyword:

How does the "this" keyword work?

`var x = function()` vs. `function x()` — Function declaration syntax

var functionName = function() {} vs function functionName() {}

`(function(){`…`})()` — IIFE (Immediately Invoked Function Expression)

What is the purpose?, How is it called?
Why does (function(){…})(); work but function(){…}(); doesn't?
(function(){…})(); vs (function(){…}());
shorter alternatives:
- !function(){…}(); - What does the exclamation mark do before the function?
- +function(){…}(); - JavaScript plus sign in front of function expression
- !function(){ }() vs (function(){ })(), ! vs leading semicolon
(function(window, undefined){…}(window));

`someFunction()()` — Functions which return other functions

Two sets of parentheses after function call

`=>` — Equal sign, greater than: arrow function expression syntax

What's the meaning of "=>" (an arrow formed from equals & greater than) in JavaScript?

`|>` — Pipe, greater than: Pipeline operator

What does the "|>" operator do in JavaScript?

`function`, `yield`, `yield` — Star after `function` or `yield`: generator functions

What is "function*" in JavaScript?
What's the yield keyword in JavaScript?
Delegated yield (yield star, yield *) in generator functions

`[]`, `Array()` — Square brackets: array notation

What’s the difference between "Array()" and "[]" while declaring a JavaScript array?
What is array literal notation in javascript and when should you use it?

If the square brackets appear on the left side of an assignment ([a] = ...), or inside a function's parameters, it's a destructuring assignment.

`{key: value}` — Curly brackets: object literal syntax (not to be confused with blocks)

What do curly braces in JavaScript mean?
Javascript object literal: what exactly is {a, b, c}?
What do square brackets around a property name in an object literal mean?
How does this object method definition work without the "function" keyword? (ES2015 Method definitions)

If the curly brackets appear on the left side of an assignment ({ a } = ...) or inside a function's parameters, it's a destructuring assignment.

`…`${`…`}`…` — Backticks, dollar sign with curly brackets: template literals

What does this `…${…}…` code from the node docs mean?
Usage of the backtick character (`) in JavaScript?
What is the purpose of template literals (backticks) following a function in ES6?

`/`…`/` — Slashes: regular expression literals

Meaning of javascript text between two slashes

`$` — Dollar sign in regex replace patterns: `$$`, `$&`, $`, `$'`, `$n`

JavaScript replace() method dollar signs

`()` — Parentheses: grouping operator

MDN: Grouping operator

Property-related expressions

`obj.prop`, `obj[prop]`, `obj["prop"]` — Square brackets or dot: property accessors

JavaScript property access: dot notation vs. brackets?

`?.`, `?.[]`, `?.()` — Question mark, dot: optional chaining operator

Question mark after parameter
Null-safe property access (and conditional assignment) in ES6/2015
Optional Chaining in JavaScript
Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?
Is there a "null coalescing" operator in JavaScript?

`::` — Double colon: bind operator

JavaScript double colon (bind operator)

`new` operator

What is the 'new' keyword in JavaScript?
What is "new.target"?

`...iter` — Three dots: spread syntax; rest parameters

(...rest) => {} — What is the meaning of “…args” (three dots) in a function definition?
fn(...args) — What is the meaning of “foo(…arg)” (three dots in a function call)?
[...iter] — javascript es6 array feature […data, 0] “spread operator”
{...props} — Javascript Property with three dots (…), What does the '…rest' stand for in this object destructuring?

Increment and decrement

`++`, `--` — Double plus or minus: pre- / post-increment / -decrement operators

++someVariable vs someVariable++ in Javascript

Unary and binary (arithmetic, logical, bitwise) operators

`delete` operator

What is the purpose of the delete operator in Javascript?

`void` operator

What does `void 0` mean?

`+`, `-` — Plus and minus: addition or concatenation, and subtraction operators; unary sign operators

What does = +_ mean in JavaScript, Single plus operator in javascript
What's the significant use of unary plus and minus operators?
Why is [1,2] + [3,4] = "1,23,4" in JavaScript?
Why does JavaScript handle the plus and minus operators between strings and numbers differently?

`|`, `&`, `^`, `~` — Single pipe, ampersand, circumflex, tilde: bitwise OR, AND, XOR, & NOT operators

What do these JavaScript bitwise operators do?
How to: The ~ operator?
Is there a & logical operator in Javascript
What does the "|" (single pipe) do in JavaScript?
What does the operator |= do in JavaScript?
What does the ^ (caret) symbol do in JavaScript?
Using bitwise OR 0 to floor a number, How does x|0 floor the number in JavaScript?
Why does ~1 equal -2?
What does ~~ ("double tilde") do in Javascript?
How does !!~ (not not tilde/bang bang tilde) alter the result of a 'contains/included' Array method call? (also here and here)

`%` — Percent sign: remainder operator

What does % do in JavaScript?

`&&`, `||`, `!` — Double ampersand, double pipe, exclamation point: logical operators

Logical operators in JavaScript — how do you use them?
Logical operator || in javascript, 0 stands for Boolean false?
What does "var FOO = FOO || {}" (assign a variable or an empty object to that variable) mean in Javascript?, JavaScript OR (||) variable assignment explanation, What does the construct x = x || y mean?
Javascript AND operator within assignment
What is "x && foo()"? (also here and here)
What is the !! (not not) operator in JavaScript?
What is an exclamation point in JavaScript?

`??` — Double question mark: nullish-coalescing operator

How is the nullish coalescing operator (??) different from the logical OR operator (||) in ECMAScript?
Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?
Is there a "null coalescing" operator in JavaScript?

`**` — Double star: power operator (exponentiation)

x ** 2 is equivalent to Math.pow(x, 2)
Is the double asterisk ** a valid JavaScript operator?
MDN documentation

Equality operators

`==`, `===` — Equal signs: equality operators

Which equals operator (== vs ===) should be used in JavaScript comparisons?
How does JS type coercion work?
In Javascript, <int-value> == "<int-value>" evaluates to true. Why is it so?
[] == ![] evaluates to true
Why does "undefined equals false" return false?
Why does !new Boolean(false) equals false in JavaScript?
Javascript 0 == '0'. Explain this example
Why false == "false" is false?

`!=`, `!==` — Exclamation point and equal signs: inequality operators

!= vs. !==
What is the difference between != and !== operators in JavaScript?

Bit shift operators

`<<`, `>>`, `>>>` — Two or three angle brackets: bit shift operators

What do these JavaScript bitwise operators do?
Double more-than symbol in JavaScript
What is the JavaScript >>> operator and how do you use it?

Conditional operator

…`?`…`:`… — Question mark and colon: conditional (ternary) operator

Question mark and colon in JavaScript
Operator precedence with Javascript Ternary operator
How do you use the ? : (conditional) operator in JavaScript?

Assignment operators

`=` — Equal sign: assignment operator

What is the difference between the `=` and `==` operators and what is `===`? (Single, double, and triple equals)

This symbol is also used for default parameters or default values in a destructuring assignment:

what does (state = {}) => state means
What does ({"key": "value"} = {}) syntax mean inside a JavaScript function

`%=` — Percent equals: remainder assignment

Having Confusion with Modulo operator

`+=` — Plus equals: addition assignment operator

How does += (plus equal) work?

`&&=`, `||=`, `??=` — Double ampersand, pipe, or question mark, followed by equal sign: logical assignments

What purpose do &&=, ||= and ??= serve?
Replace a value if null or undefined in JavaScript
Set a variable if undefined
Ruby’s ||= (or equals) in JavaScript?
Original proposal
Specification

`<<=`, `>>=`, `>>>=`, `&=`, `^=`, `|=` — Double less than, double greater than, triple greater than, ampersand, caret, or pipe followed by equal sign: bitwise assignments

What do these JavaScript bitwise operators do?

Destructuring

of function parameters: Where can I get info on the object parameter syntax for JavaScript functions?
of arrays: Multiple assignment in javascript? What does [a,b,c] = [1, 2, 3]; mean?
of objects/imports: Javascript object bracket notation ({ Navigation } =) on left side of assign

Comma operator

`,` — Comma operator (not to be confused with the comma used in variable declarations)

What does a comma do in JavaScript expressions?
Comma operator returns first value instead of second in argument list?
When is the comma operator useful?

Control flow

`{`…`}` — Curly brackets: blocks (not to be confused with object literal syntax)

JavaScript curly braces with no function or json

Declarations

`var`, `let`, `const` — Declaring variables

What's the difference between using "let" and "var"?
Are there constants in JavaScript?
What is the temporal dead zone?
var a, b; — Comma used in variable declarations (not to be confused with the comma operator): JavaScript variable definition: Commas vs. Semicolons

Label

`label:` — Colon: labels

What does the JavaScript syntax foo: mean?
What does ':' (colon) do in JavaScript?

Other

`123n` — `n` after integer: BigInt

What does character 'n' after numeric literal mean in JavaScript?

`#` — Hash (number sign): Private methods or private fields

What does the # symbol do in JavaScript?

`_` — Underscore: separator in numeric literals

Javascript numeric separators?
Is there a Javascript equivalent to the Ruby syntax using underscores (e.g. 10_000 = 10000) to make larger integers human readable?

What does it mean $ and $$ in javascript?

The whole code is just a function call with two arguments:

;(function( $, $$ ){ 'use strict';
  // skipped
})(
  typeof jQuery !== 'undefined' ? jQuery : null,
  typeof cytoscape !== 'undefined' ? cytoscape : null
);

The first argument is jQuery global variable (or null, if jQuery is undefined), and the second is cytoscape global variable (or null, if is undefined).