Javascript method for determining whether a variable has a value _ javascript skills

This article mainly introduces the javascript method for determining whether a variable has a value. It can effectively determine the value, which is of great practical value, for more information about how to use javascript to determine whether a variable has a value, see the example in this article. Share it with you for your reference. The specific analysis is as follows:

For example:

Var a = null; var B = undefined;

The two cases above are regarded as null.

If (! = Null &! = Undefined) {//} // Why cannot I use if (! = Null) {//} var a;! = Null; // true // Why cannot I use if (! = Undefined) {//} var a = null;! === Undefined; // true

I hope this article will help you design javascript programs.