JavaScript Keywords | List of Reserved Words

Keywords in JavaScript are pre-defined words that have specific meanings to the interpreter and that meanings cannot be changed. They are also called reserved words in JavaScript.

JavaScript provides a set of reserved keywords that are the part of syntax in the JavaScript language.

JavaScript’s keywords are used to perform actions in the program. For example, the let keyword tells the browser to create a variable:

let x = 10;

Here, let is a keyword that indicates that x is the name of a variable that stores a value 10.

Since keywords have specific meaning in JavaScript language, we cannot use them to define variables, functions, or labels that have the same names as these keywords. For example:

let const = 20; // Invalid, here, const cannot be a variable name because const is a keyword that is used to store a constant value.

Since JavaScript is a case-sensitive language, all keywords in JavaScript must be written in lowercase letters (small letters).

List of JavaScript Keywords (Reserved Words)


Table shows the list of commonly used total number of keywords (reserved words) in the JavaScript language. They are as follows:

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

Note: Reserved words marked with* are new in ECMAScript 5 and 6.

Removed Reserved Words


The following JavaScript keywords have been removed from the ECMAScript 5/6 standard:

abstract boolean byte char double final
float goto int long native short
synchronized throws transient volatile

Note: Do not use these removed reserved words to define the name of variables. ECMAScript 5/6 does not have full support in all web browsers.

JavaScript Objects, Properties, and Methods


You should also abstain to using the name of pre-defined JavaScript objects, properties, and methods:

Array Date eval function hasOwnProperty Infinity
isFinite isNaN isPrototypeOf length Math NaN
name Number Object prototype String toString
undefined valueOf

In this tutorial, you learned a list of all JavaScript keywords (reserved words) that should not be used as variables, functions, or labels names. Hope that you will have understood all the basic points related to JavaScript reserved words.
Thanks for reading!!!