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JavaScript Implementations

Although ECMAScript is an important standard, it is not the only part of JavaScript, and certainly not

the only part that has been standardized. Indeed, a complete JavaScript implementation is made up of

three distinct parts (see Figure 1-1):

The Core (ECMAScript)

The Document Object Model (DOM)

The Browser Object Model (BOM)

Figure 1-1

ECMAScript

doesn’t have ties to any browser in particular and, actually, has no methods for user input

or output to speak of. (It is not unlike languages such as C, which rely on external libraries to accomplish

such tasks.) So what is ECMAScript? ECMA-262 (p. 2) describes it like this:

“ECMAScript can provide core scripting capabilities for a variety of host environments, and therefore

the core scripting language is specified...apart from any particular host environment.”

A Web browser is considered a host environment for ECMAScript, but it is not the only host environment.

Indeed, numerous other environments (such as Nombas’s ScriptEase and Macromedia’s ActionScript,

used in both Flash and Director MX) can host ECMAScript implementations. So what does ECMAScript

specify outside of a browser? To put it simply, ECMAScript describes the following:

Syntax

Types

Statements

Keywords

Reserved Words

Operators

Objects

ECMAScript is simply a description, defining all the properties, methods, and objects of a scripting lan-

guage. Other languages implement ECMAScript, as JavaScript does (see Figure 1-2), as the baseline for

functionality.

JavaScript

ECMAScript DOM

BOM

What Is JavaScript?

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