JavaScript reserved words

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.

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

<!DOCTYPE html>
<html>
<head>
<title>JS is fun :)</title>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<script>
const name = "John Doe";
let age = 200;
function printName(){
console.log(name+ " "+ age);
}
</script>
</body>
</html>
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.