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Native objects

Types of Objects

In ECMAScript, all objects are not created equal. Generally speaking, three specific types of objects can

be used and/or created.

Native objects

ECMA-262 defines

native objects

as “any object supplied by an ECMAScript implementation indepen-

dent of the host environment.” Simply put, native objects are the classes (reference types) defined by

ECMA-262. They include all the following:

Object Function Array String

Boolean Number Date RegExp

Error EvalError RangeError ReferenceError

SyntaxError TypeError URIError

Some of these native objects you are already familiar with from the previous chapter (

Object

Function

String

Boolean

, and

Number

), and some will be discussed later in the book. For now, the two native

objects of importance are

Array

and

Date

The Array class

In ECMAScript, unlike in Java, there is an actual

Array

class. You create an

Array

object like this:

var aValues = new Array();

If you know ahead of time how many items you need in the array, you can pass in the array size as a

parameter:

var aValues = new Array(20);

Using either of these two methods, you must populate the array by using bracket notation, similar to

how it is done in Java:

var aColors = new Array();

aColors[0] = “red”;

aColors[1] = “green”;

aColors[2] = “blue”;

Here, an array is created and given three items,

“red”

“green”

, and

“blue”

. The array dynamically

grows in size with each additional item

Also, if you know the values that the array should contain, you can specify those as arguments, creating

Array

object with a length equal to the number of arguments. For example, the following line of code

creates an array of three strings:

var aColors = new Array(“red”, “green”, “blue”);

Chapter 3

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