Null和Undefined是JavaScript里面的两种数据类型。
Undefined is a variable that has been declared but not assigned a value.
null to any variable which basically means it’s blank.
explicitly empty.
Null and Undefined
null. That must be done by you in your code.
Let’s get some more info on these.
Typeof null and undefined
undefined.
Comparison Using Abstract and Strict Equality
false.
Comparison between null and undefined
true.
So JavaScript does consider these to be relatively equal since they both represent an empty value.
undefined, you can check for abstract equality and compare it to either null or undefined. Both will return the same result.
转载自：https://levelup.gitconnected.com/javascript-null-vs-undefined-2acda986f79f