undefined property

When discussing the raw data types in JavaScript, most people know the basics from string, number to Boolean. These primitive types are fairly simple and behave in a common sense. However, this article will focus more on the unique raw data types

A bad time to answer, especially undefined, because this involves the realization of the principle of undefined. So, after thinking carefully, write down this article, please heroes to shoot bricks. Total known: null = = undefined However: null!==

Performance improvement and analysis of Web page special effects undefined At work we often need to determine whether a variable/attribute is undefined. There are usually two ways of writing1//Mode 12 typeof age = = ' undefined ';34//Mode 25 Age = =

JS Judge undefined type Today, you use ShowModalDialog to open the page and return the value. The return value is undefined when the open page clicks the Close button or closes the direct point on the browserSo be smart and judge. var

  This article is mainly on the JS to determine the type of undefined, undefined,null,nan the difference between the detailed analysis of the introduction, the need for friends can come to the reference, I hope to help you. JS judge undefined type

1. Type analysis :The data type in JS has 5 kinds of undefined,boolean,number,string,object, the first 4 is the original type, and the 5th type is reference.Code Copy Code code as follows: var A1; var a2 = true; var a3 = 1; var

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

In JavaScript development, people ask: What's the difference between null and undefined? A bad time to answer, especially undefined, because this involves the realization of the principle of undefined. So, after thinking carefully, write down this

1. Type analysis:JS data types have undefined,boolean,number,string,object, such as 5, the first 4 are the original type, the 5th is the reference type.CodeCode highlighting produced by Actipro Codehighlighter (freeware)

js judging undefined typeToday you use ShowModalDialog to open a page and return a value. When opening a page click the Close button or direct point on the browser close then the return value is undefinedso smart to judgevar