Null and undifined for JavaScript

Null represents an object, or the value of a variable is null, undifined means that an object (variable) is declared, not initialized to him, or the object (variable) is not declared at all.

1, NULL is the JavaScript keyword undifined not.

2, typeof return string, there are six possible: "Number", "string", "Boolean", "Object", "function", "undefined"

typeof NULL returns the result as "object", indicating that null is an object. The return result of TypeOf undifined is "undifined".

3, null==undifined result is true,null===undifined result is false.

In addition, to determine whether an object exists, you can use TypeOf a!=undifined to judge. Returns true if the variable a exists.

Remember, you cannot judge by if (a), so you may get an error "uncaught referenceerror:a is not defined"

Null and undifined for JavaScript