javascript if variable null

JavaScript itself does not determine whether a variable is a null function, because the variable may be string,object,number,boolean and other types, different types, and the judging method is different. So in the article wrote a function, to

1) Intro Not long ago I set up a technology group in a MM asked a question like this, she posted the code as follows: var a = 1;function hehe (){Window.alert (a);var a = 2;Window.alert (a);}Hehe (); The results of the execution are as follows:

JavaScript Learning record day6-function variable scope, deconstruction assignment and method@ (learning) [JavaScript][TOC]1. ScopeIn JavaScript, variables that are var declared are actually scoped.If a variable is declared inside the function body,

False, zero, null, undefined, and empty string objects in Javascript In Javascript, We often come into contact with the five special objects mentioned in the question -- false, 0, empty string, NullAnd undefined. These objects are easy to use

When discussing the primitive data types in Javascript, most people know the basic knowledge, from String, Number to Boolean. These primitive types are quite simple and behavior is common sense. However, this article will focus more on the unique

ArticleDirectory Javascript Introduction How to Implement Javascript Where to place Javascript Javascript statements Javascript Variables Javascript Operators Javascript branch statement Javascript message box

if (judgment expression) {Execute content}If the expression is true, the contents of the parentheses are executed.Here, if the variable is not 0,null,undefined,false, it will be handled as true. As long as the variable has a value other than 0 or an

Most computer languages have and have only one value that denotes "none", such as the nil of the None,ruby language of the Null,python language of the C language Null,java language. Oddly enough, the JavaScript language actually has two values that

This article mainly introduces the Null and Undefined primitive data types in javascript. If you need them, you can refer to the basic knowledge that most people know when discussing the primitive data types in JavaScript, from String, Number to

Front. The General program language, which indicates null only NULL, but JavaScript designer Brendan Eich but designed a undefined, which undoubtedly increased the complexity of the program, but there are some reasons for this. This article