Reserved keywords in JavaScript
JavascriptReserved WordsJavascript Problem Overview
What JavaScript keywords (function names, variables, etc) are reserved?
Javascript Solutions
Solution 1 - Javascript
Here is my poem, which includes all of the reserved keywords in JavaScript, and is dedicated to those who remain honest in the moment, and not just try to score:
Let this long package float,
Goto private class if short.
While protected with debugger case,
Continue volatile interface.
Instanceof super synchronized throw,
Extends final export throws.
Try import double enum?
- False, boolean, abstract function,
Implements typeof transient break!
Void static, default do,
Switch int native new.
Else, delete null public var
In return for const, true, char
…Finally catch byte.
Solution 2 - Javascript
We should be linking to the actual sources of info, rather than just the top google hit.
http://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Reserved_Words
JScript 8.0: http://msdn.microsoft.com/en-us/library/ttyab5c8.aspx
Solution 3 - Javascript
To supplement benc's answer, see Standard ECMA-262. These are the official reserved words, but only a pedant ignores the implementation to respect the standard. For the reserved words of the most popular implementations, that is firefox and internet explorer, see benc's answer.
The reserved words in EMCAScript-262 are the Keywords, Future Reserved Words, NullLiteral, and BooleanLiterals, where the Keywords are
break do instanceof typeof
case else new var
catch finally return void
continue for switch while
debugger function this with
default if throw
delete in try
the Future Reserved Words are
abstract export interface static
boolean extends long super
byte final native synchronized
char float package throws
class goto private transient
const implements protected volatile
double import public
enum int short
the NullLiteral is
null
and the BooleanLiterals are
true
false
Solution 4 - Javascript
I was just reading about this in JavaScript & jQuery: The Missing Manual:
> Not all of these reserved words will cause problems in all browsers, but it’s best to steer clear of these names when naming variables.
>
> JavaScript keywords: break, case, catch, continue, debugger, default, delete, do, else, false, finally, for, function, if, in, instanceof, new, null, return, switch, this, throw, true, try, typeof, var, void, while, with
.
>
> Reserved for future use: abstract, boolean, byte, char, class, const, double, enum, export, extends, final, float, goto, implements, import, int, interface, let, long, native, package, private, protected, public, short, static, super, synchronized, throws, transient, volatile, yield
.
>
> Pre-defined global variables in the browser: alert, blur, closed, document, focus, frames, history, innerHeight, innerWidth, length, location, navigator, open, outerHeight, outerWidth, parent, screen, screenX, screenY, statusbar, window
.
Solution 5 - Javascript
Here is a browser and language version agnostic way to determine if a particular string is treated as a keyword by the JavaScript engine. Credits to this answer which provides the core of the solution.
function isReservedKeyword(wordToCheck) {
var reservedWord = false;
if (/^[a-z]+$/.test(wordToCheck)) {
try {
eval('var ' + wordToCheck + ' = 1');
} catch (error) {
reservedWord = true;
}
}
return reservedWord;
}
Solution 6 - Javascript
None of the current answers warn that regardless of ES-Dialect, browsers tend to have their own lists of reserved keywords, methods etc on top of what ES dictates.
For example, IE9 prohibits use of logical names like: addFilter
, removeFilter
(they, among others, are reserved methods).
See http://www.jabcreations.com/blog/internet-explorer-9 for a more extensive 'currently known' list specific to IE9. I have yet find any official reference to them on msdn (or elsewhere).
Solution 7 - Javascript
Here is a list from Eloquent JavaScript book:
break
case
catch
class
const
continue
debugger
default
delete
do
else
enum
export
extend
false
finally
for
function
if
implements
import
in
instanceof
interface
let
new
null
package
private
protected
public
return
static
super
switch
this
throw
true
try
typeof
var
void
while
with
yield
Solution 8 - Javascript
benc's answer is excellent, but for my two cents, I like the w3schools' page on this:
http://www.w3schools.com/js/js_reserved.asp
In addition to listing the keywords reserved by the standard, it also has a long list of keywords you should avoid in certain contexts; for example, not using the name alert
when writing code to be run in a browser. It helped me figure out why certain words were highlighting as keywords in my editor even though I knew they weren't keywords.