JavaScript reserved Keywords

Source: Internet
Author: User
JavaScript reserved Keywords

In JavaScript, some identifiers are reserved keywords and cannot be used as variable names or function names. JavaScript Standard

All modern browsers fully support ECMAScript 3 (Es3,javascript's third edition, starting from 1999).

ECMAScript 4 (ES4) was not approved.

ECMAScript 5 (released in es5,2009) is the latest official version of JavaScript.

As time goes on, we begin to see that all modern browsers have fully supported ES5.

JavaScript reserved Keywords

A reserved keyword for Javascript may not be used as a variable, label, or function name. Some reserved keywords are used as Javascript for later expansion.

Abstract Arguments Boolean Break Byte
Case Catch Char class* Const
Continue Debugger Default Delete Todo
Double Else enum* Eval export*
extends* False Final Finally Float
For function Goto If Implements
import* In instanceof Int Interface
Let Long Native New Null
Package Private Protected Public Return
Short Static super* Switch Synchronized
This Throw Throws Transient True
Try typeof Var void Volatile
While With Yield

* The keyword for the tag is newly added in ECMAScript5. JavaScript objects, properties, and methods

You should also avoid using JavaScript-built names of objects, properties, and methods as a variable or function name for javascript:

Array Date Eval function hasOwnProperty
Infinity Isfinite isNaN isPrototypeOf Length
Math NaN Name Number Object
Prototype String Tostring Undefined valueof

Java reserved Keywords

JavaScript is often used in conjunction with Java. You should avoid using some Java objects and properties as JavaScript identifiers:

GetClass Java Javaarray Javaclass Javaobject Javapackage

Windows reserved Keywords

JavaScript can be used outside of HTML. It can be used as a programming language in many other applications.

In HTML, you must (you should also do this for portability) avoid using the names of HTML and Windows objects and properties as Javascript variables and function names:

Alert All Anchor Anchors Area
Assign Blur button CheckBox Clearinterval
Cleartimeout Clientinformation Close Closed Confirm
Constructor Crypto decodeURI decodeURIComponent Defaultstatus
Document Element Elements Embed Embeds
encodeURI encodeURIComponent Escape Event FileUpload
Focus Form Forms Frame Innerheight
Innerwidth Layer Layers Link Location
Mimetypes Navigate Navigator Frames Framerate
Hidden History Image Images Offscreenbuffering
Open Opener Option Outerheight Outerwidth
Packages Pagexoffset pageYOffset Parent Parsefloat
parseint Password Pkcs11 Plugin Prompt
Propertyisenum Radio Reset ScreenX ScreenY
Scroll Secure Select Self SetInterval
SetTimeout Status Submit Taint Text
TextArea Top Unescape Untaint Window

HTML Event Handle

In addition, you should avoid using the name of an HTML event handle as a Javascript variable and function name.


Onblur OnClick OnError onfocus
OnKeyDown onkeypress OnKeyUp onmouseover
OnLoad OnMouseUp OnMouseDown OnSubmit

non-standard JavaScript

In addition to reserved keywords, there are some non-standard keywords in the JavaScript implementation.

One instance is the const keyword, which is used to define variables. Some JavaScript engines treat const as synonymous with Var. Other engines define the const as a read-only variable.

Const is an extension of JavaScript. The JavaScript engine supports it in Firefox and Chrome. But it is not part of JavaScript standard ES3 or ES5. Recommendation: Do not use it .

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