javascript if variable null

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JavaScript determines if a variable is not a null value

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

Talk about some difficult problems in JavaScript grammar (i.)

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

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

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

Explore the abyss of Null and Undefined in JavaScript

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

Basic JavaScript knowledge

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

The difference between if (variable) and if (variable ==true) in JavaScript

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

The difference between undefined and null in JavaScript _javascript skills

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

Explanation of the original javascript data types Null and Undefined_javascript skills

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

Undefined and Null analysis of JavaScript type system _javascript skills

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

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