JavaScript must know (ii) NULL and UNDEFINED_JAVASCRIPT techniques

Null

NULL represents a "null",

Use typeof (null);//object; Indicate that he is a special object.

A null type is only its own unique member. He does not contain attributes and methods.

Undefined

Undefined also means "empty",

The use of typeof (undefined),//undefined, indicates that he is undefined type.

The undefined type contains only one member of itself, and he does not contain attributes and methods.

Summary

Null and undefined can be the same in the MO, for example, can be converted to a Boolean value, to represent false;

Null and undefined are not available. and [] to take member values, so you should first determine whether the object is null or undefined.