Keywords in JavaScript Tutorial

In this section, we will learn what the keywords in JavaScript are and how they work.

Note: Before reading this section, you need to be familiar with the JavaScript variables in general.

What are Keywords in JavaScript?

The JavaScript language has a couple of special keywords that we use them for specific purposes in the language.

So because these keywords are reserved for the JavaScript itself, using them is forbidden as the name of a variable in the JavaScript programs.

JavaScript Reserved Words

In the list below you can see all these keywords:

abstract

arguments

await

boolean

break

byte

case

catch

char

class

const

continue

debugger

default

delete

do

double

else

enum

eval

export

extends

false

final

finally

float

for

function

goto

if

implements

import

in

instanceof

int

interface

let

long

native

new

null

package

private

protected

public

return

short

static

super

switch

synchronized

this

throw

throws

transient

true

try

typeof

var

void

volatile

while

with

yield

Since the ECMAScript 5/6, some of the keywords mentioned in the table above are removed. These words are mentioned in the table below:

Although this means we can use them as the name of a variable, it is recommended to not to. This is because still a considerable portion of people in the world are using the older version of web browsers that don’t support the `ECMAScript 5/6`.

Here’s the list:

abstract

boolean

byte

char

double

final

float

goto

int

long

native

short

synchronized

throws

transient

volatile

Also there are a couple of built-in Objects, methods, functions and properties in the JavaScript that we should avoid overriding them as the name of a variable.

Here’s the list of these JavaScript built in materials:

Array

Date

eval

function

hasOwnProperty

Infinity

isFinite

isNaN

isPrototypeOf

length

Math

NaN

name

Number

Object

prototype

String

toString

undefined

valueOf

In production environment, we usually mix other languages with the JavaScript. So you should also be careful and avoid using variable names that might be a special word in other programming languages that you use along with the JavaScript.

Example: using JavaScript reserved words

const name = "John Doe"; 
let age = 200; 
function printName(){
  console.log(name+ " "+ age);
}

Output:

John Doe 200

As you can see, we’ve used a few JavaScript keywords for their special purposes and not for the variable names!

Note: you’ll learn most of these keywords in the future sections.

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