JavaScript null empty value

　JavaScript 전역 속성/함수

null valueindicating the intentional absence of any object value.

It is JavaScript'sOne of the primitive types.

The null value is not an identifier of a global object property, such as undefined. On the contrary, null indicates the absence of an identifier, indicating that the variable does not point to any object.

Syntax:

null

var str;
if (str == null) {
　　　//　str is null
} else {
　　　//　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, because the former performs type conversion.

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

브라우저 호환성

모든 브라우저는 null 값을 완벽히 지원합니다:

기술 세부 사항

더 많은 예제

주어진 문자열이 [aeiou] 문자를 포함하지 않으면 getVowels() 함수는 0을 반환합니다:

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

　JavaScript 전역 속성/함수