continues until the end of the line. They are only valid at the start of

files and are intended for use in CLI environments.cite-ref-4[4]

#! Hashbang comment

// One-line comment

/* Multi-line

comment */

Variables in standard JavaScript have no type attached, so any value

(each value has a type) can be stored in any variable. Starting with

ES6, the 6th version of the language, variables could be declared with

var for function scoped variables, and let or const which are for

block level variables. Before ES6, variables could only be declared with

a var statement. Values assigned to variables declared with const cannot

be changed, but their properties can. var should no longer be used since

let and const are supported by modern browsers.cite-ref-5[5] A variable's

identifier must start with a letter, underscore (_), or dollar sign ($),

while subsequent characters can also be digits (0-9). JavaScript is case

sensitive, so the uppercase characters "A" through "Z" are different

from the lowercase characters "a" through "z".

Starting with JavaScript 1.5, ISO 8859-1 or Unicode letters (or \uXXXX

Unicode escape sequences) can be used in identifiers.cite-ref-6[6] In certain

JavaScript implementations, the at sign (@) can be used in an

identifier, but this is contrary to the specifications and not supported

in newer implementations.

Variables declared with var are lexically scoped at a function level,

while ones with let or const have a block level scope. Since

declarations are processed before any code is executed, a variable can

be assigned to and used prior to being declared in the code.cite-ref-7[7] This is

referred to as hoisting, and it is equivalent to variables being