null和undefined的区别？

1.数据类型不一样

console.log(typeof(undefined));//undefined
console.log(typeof(null));//object

2.转化值时不一样undefined：NaN，null：0

undefined：
console.log(Number(undefined));//NaN
console.log(Number(1+undefined));//NaN
null：
console.log(Number(null));//0
console.log(Number(1+null));//1

3.比较时结果不一样

undefined === null;//false
undefined == null;//true