25 Answers · test(null) => true test(undefined) => true test(0) => false test(1) => false test(true) => false test(false) => false test('s') => ... ... <看更多>

The primitive values null and undefined have a distinct difference that should be used. But how to you tell ... ... <看更多>

Checking for either. Fact is you will need to deal with both. Interestingly in JavaScript with == , null and undefined are only equal to each other:. ... <看更多>

To check if a value is null , you use the strict equality operator ... Besides false , 0 , an empty string ( '' ), undefined , NaN , null is a falsy value. ... <看更多>

함수의 반환이 명시적으로 없으면 undefined를 반환합니다. 원시 자료형 중 하나. // test default let test; console.log('variable test is ' + ... ... <看更多>