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Object class

This syntax is similar to Java, although ECMAScript requires parentheses to be used only if there are one

or more parameters. If there are no parameters, such as in the previous line of code, then the parentheses

can be safely omitted:

var o = new Object;

Chapter 3, “Object Basics,” contains a more in-depth look at objects and their behaviors. This section

focuses on those reference types that have primitive equivalents.

The Object class

The

Object

class itself isn’t very useful, but you should understand it before moving on to the other

classes. Why is that? Because the

Object

class in ECMAScript is similar to

java.lang.Object

in Java:

It is the base class from which all ECMAScript classes inherit. All the properties and methods of the

Object class are also present in the other classes, and so to understand the

Object

class is to understand

all the others better.

The

Object

class has the following properties:

constructor

— A reference value (pointer) to the function that created the object. For the

Object

class, this points to the native

Object()

function.

prototype

— A reference value to the object prototype for this object. Prototypes are discussed

further in Chapter 3. For the all classes, this returns an instance of

Object

by default.

The

Object

class also has several methods:

hasOwnProperty(

property

)

— Determines if a given property exists for the object. The

property must be specified as a string (for example,

o.hasOwnProperty(“name”)

isPrototypeOf(

object

)

— Determines if the object is a prototype of another object.

propertyIsEnumerable(

property

)

— Determines if a given property can be enumerated by

using the

for...in

statement (discussed later in this chapter).

toString()

— Returns a primitive string representation of the object. For the

Object

class,

this value is undefined in ECMA-262 and, as such, differs in each implementation.

valueOf()

— Returns the most appropriate primitive value of this object. For many classes,

this returns the same value as

toString()

Each of the properties and methods listed previously are designed to be overridden by other classes.

Although the parentheses aren’t required, it’s always best to include them in order

to avoid confusion.

Chapter 2

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