javascript test if defined

Document directory 1.4. Javascript in other contexts 1.4. Javascript in other environments 1.5. processing Javascript 1.5. go deep into Javascript Statement: translation has only one purpose: learning purposes. If you have any copyright

Directory1 History 2 clarifying misunderstandings 3 basic concepts 4 features 5 different from Java 6 development toolsHistoryProbably in 1992, a company called Nombas began developing an embedded scripting language called C-minus (C-minus-minus, or

Scope of the variableA variable's scope (scope) is the area in the program that defines the variable.Global variables scope (scope) is global, that is, in JavaScript code, it is defined everywhere.Variables declared within a function are defined

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:

The things that every JavaScript developer should know2015-06-07 front-end Daquan(Click the blue Word above to quickly follow us)JavaScript is a growing language, especially now that the ECMAScript specification is published on an annual release

JavaScript is a widely used scripting language for Web client development, often used to control the browser's DOM tree and add dynamic functionality to HTML pages. The Web standard that JavaScript adheres to today is ECMAScript262. Because

We cannot explain all the details of JavaScript in a blog. If you are more or less involved in web application development, our Java tools and technical scope reports reveal that most (71%) Java developers are classified into this category, but you

1th Chapter Essence Some of the features of JavaScript feature a lot more trouble than they are worth. Some of these features are because the specification is so imperfect that it can cause portability problems; Some features can lead to the

varVar1;console.log (typeofVAR0);//print "Undefined", the main look under the face of var0 separate outputConsole.log (typeofVAR1);//print "undefined"Console.log (typeof true);//print "Boolean"Console.log (typeof false);//print "Boolean"Console.log (

When I read the jQuery source code, I often think that those factors will make me unable to read the code. Which of the most critical factors is the earliest thought of as the architectural design of jQuery, when I finally found the jQuery