JavaScript null null value

　JavaScript Global Properties/Function

null valuerepresenting the intentional absence of any object value.

It is JavaScript'sOne of the primitive types.

The null value is not an identifier for a global object property, such as undefined. Instead, null represents a lack of identification, indicating that the variable does not point to any object.

Syntax:

null

var str;
if (str == null) {
　　　//　str is null
}
　　　//　str is not null
}

The difference between null and undefined

The values of null and undefined are equal, but the types are different.

When checking null or undefined, please note the difference between equals (==) and identity (===) operators, as the former performs type coercion.

typeof null　　//　"object" (due to legacy reasons, it is not "null")
typeof undefined　//　"undefined"
null == undefined//　true
null === undefined　　　//　false

Browser Compatibility

All browsers fully support null values:

Technical Details

More Examples

If the given string does not contain [aeiou] letters, the getVowels() function will return 0:

function getVowels(str) {
　　　var x = str.match(/[aeiou]/gi);
　　　if (x === null) {
　　　　　　return 0;
　　　}
　　　return x.length;
}

　JavaScript Global Properties/Function