The difference between null and undefined

Java Object Class is the parent of all classes , in other words Java All classes of inherit Object, Subclasses can use Object All the ways .

null and undefined The difference between

1、 First, the data types are different

console.log(typeof null) //object

console.log(typeof undefined) //undefined

2、null and undefined Both equal , But when the two make a congruent comparison , The two are not equal .（ Because their data types are different ）

console.log(null==undefined) //ture

console.log(null===undefined) //false

3、 Converted to different numbers

console.log(Number(null)) //0

console.log(Number(undefined)) //NaN

console.log(Number(22+null)) //22

console.log(Number(22+undefined)) //NaN

 4、null representative “ empty ”, For null pointer ;undefined Is defined without assignment

var a;

console.log(a);//undefined

var b=null;

console.log(b);//null