javascript test if undefined

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JavaScript type system--undefined and NULL

Previous wordsGeneral programming language, which means null only, but JavaScript designer Brendan Eich design a undefined, which undoubtedly increases the complexity of the program, but there are some reasons for this. This article will detail the

Differences between null, Nan, and undefined in Javascript

1. Type Analysis:   The data types in JS include undefined, Boolean, number, string, and object. The first four are original data types and the second are reference data types. Code Code highlighting produced by Actipro CodeHighlighter (

Js judges the undefined type and js judges the undefined type.

Js judges the undefined type and js judges the undefined type.Js determines the undefined type if (reValue = undefined){Alert ("undefined "); }The system found that the data could not be determined, and finally found the information to use the

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

The difference between null, Nan, and undefined in Javascript summary _javascript tips

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

The difference between null, Nan, and undefined in Javascript

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. Code: varA1;varA2= true;varA3= 1;varA4= "Hello";varA5= NewObject ();varA6= NULL;varA7=NaN;varA8=

JavaScript type system--undefined and NULL

xTable of Contents [1] reason [2]undefined [3]null Front wordsGeneral programming language, which means null only, but JavaScript designer Brendan Eich design a undefined, which undoubtedly increases the complexity of the program, but there are some

JavaScript type system--undefined and null comprehensive understanding of the basics

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

Summary of differences between null, NaN, and undefined in Javascript

1. Type Analysis:The data types in js include undefined, boolean, number, string, and object. The first four are original data types and the second are reference data types.Code Copy codeThe Code is as follows: var a1; Var a2 = true; Var a3 = 1; Var

The difference between null, Nan, and undefined in Javascript

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)

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