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Keywords

ECMA-262 describes a set of

keywords

that ECMAScript supports. These keywords indicate beginnings

and/or endings of ECMAScript statements. By rule, keywords are reserved and cannot be used as vari-

able or function names. Here is the complete list of ECMAScript keywords:

break else new var

case finally return void

catch for switch while

continue function this with

default if throw

delete in try

do instanceof typeof

If you use a keyword as a variable or function name, you will probably be greeted with an error message

like this: “Identifier expected.”

Reserved Words

ECMAScript also defines a number of

reserved words

. The reserved words are, in a sense, words that are

reserved for future use as keywords. Because of this, reserved words cannot be used as variable or func-

tion names. The complete list of reserved words in ECMA-262 Edition 3 is as follows:

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

If you use a reserved word as a variable or function name, more than likely you

will not

receive an

error...until a future browser implements one of them. Then the word will be considered a keyword,

and you will get a keyword error.

Primitive and Reference Values

In ECMAScript, a variable can hold one of two types of values: primitive values and reference values.

Primitive values

are simple pieces of data that are stored on the

stack

, which is to say that their

value is stored directly in the location that the variable accesses.

Reference values

, on the other hand, are objects that are stored in the

heap

, meaning that the value

stored in the variable location is a

pointer

to a location in memory where the object is stored.

ECMAScript Basics

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