Is the javascript keyword var?

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Var is the keyword in javascript, but the js keyword is not only var, but also break, else, new, case, finally, return, void, catch, for, switch, while, continue, this, with, if and so on.

The operating environment of this tutorial: windows7 system, javascript1.8.5 version, Dell G3 computer.

Javascript keyword

Keywords are a set of names (or commands) used within the JavaScript language specified by ECMA-262. These names have a specific purpose, and users cannot customize identifiers of the same name. The details are shown in the table.

ECMAScript keyword breakdeleteifthiswhilecasedointhrowwithcatchelseinstanceoftry

Continuefinallynewtypeof

Debugger (new to ECMAScript 5) forreturnvar

Defaultfunctionswitchvoid

As you can see, var is the keyword in javascript, but the keyword of js is not only var, but also break, delete, if, this, while, and so on.

Javascript reserved word

ECMA also describes another set of reserved words that cannot be used as identifiers. Although reserved words do not have any specific use in the language, they may be used as keywords in the future. The following are all reserved words defined by ECMA version 3:

Abstract 、 enum 、 int 、 short 、 boolean 、 export 、 interface 、 static 、 byte 、 extends 、 long 、 super 、 char 、 final 、 native 、 synchronized 、 class 、 float 、 package 、 throws 、 const 、 goto 、 private 、 transient 、 debugger 、 implements 、 protected 、 volatile 、 double 、 import 、 public .

Using keywords as identifiers in code is a "Identifier Expected" error in most browsers. The use of reserved words may not cause the same error, depending on the browser. In general, it is best not to use keywords and reserved words as identifiers to be compatible with future versions of ECMAScript.

The content of keywords is not immutable, with the improvement of the version of JavaScript, keywords will also change, such as ES2015 added let and const as keywords.

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