What are Variables in JavaScript

Variables are a foundational aspect of programming with JavaScript, or any programming Language.

A variable must have a unique name.


You use variables as symbolic names for values in your application.

The names of variables, called identifiers, conform to certain rules.


An identifier must start with a letter, underscore (__), or a dollar sign ($). Subsequent characters can

also be digits (0-9).

Letters include the characters “A” through “Z”

(uppercase) as well as “a” through “z” (lowercase).

Unicode letters such as å and ü can be used in identifiers. Unicode escape sequences as

characters can also be used in identifiers.


var x = 42

let y = 13

This syntax can be used to declare local and global variables.

let { bar }= foo

This will create a variable named bar and assign to it the value corresponding to the key of the same name from our object foo.


A variable declared using the var or let statement with no assigned value specified has the value of undefined.

An attempt to access undeclared variable results in a Reference Error exception being thrown:


JavaScript borrows most of its syntax from Java, C, and C++, but it has also been influenced by A wk, Perl, and Python.


JavaScript is case-sensitive.

JavaScript uses the Unicode character set.

In JavaScript, instructions are called statements and are separated by semicolons (;). It is considered best practice, to always write a semicolon after a statement, it reduces the chances of bugs getting into the code.


// a one-line comment

/* this is a longer,

*multi-line comment


/* You can’t, however, /* nest

Comments */ Syntax Error */



Declares a variable, optionally initializing it to a value.


Declares a block-scoped, local variable, optionally initializing it to a value.


Declares a block-scoped, read-only named constant.

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