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Boolean class

The Boolean class

The

Boolean

class is the reference type for the Boolean primitive type. To create a

Boolean

object, you

need only pass in a Boolean value as a parameter:

var oBooleanaobject = new Boolean(true);

Boolean

objects override the

valueOf()

method of the

Object

class to return a primitive value of

either

true

false

; the

toString()

method is also overridden to return a string of “

true”

“false”

when called. Unfortunately, not only are Boolean objects of little use in ECMAScript, they can

actually be rather confusing.

The problem typically occurs when trying to use

Boolean

objects in Boolean expressions. For example:

var oFalseObject = new Boolean(false);

var bResult = oFalseObject && true; //outputs true

In this code, a

Boolean

object is created with a value of

false

. That same object is then ANDed with

the primitive value

true

. In Boolean math,

false

AND

true

is equal to

false

. However, in this line of

code it is the

oFalseObject

being evaluated, not its value (

false

). As discussed earlier, all objects are

automatically converted to

true

in Boolean expressions, so

oFalseObject

actually is given a value of

true

in the expression. Then,

true

ANDed with

true

is equal to

true

The Number class

As you might have assumed, the

Number

class is the reference type for the Number primitive type. To

create a

Number

object, do the following:

var oNumberObject = new Number(55);

You may recognize the

Number

class from earlier in this chapter, where the special number values are

discussed (such as

Number.MAX_VALUE

). All the special values are static properties of the

Number

class.

To get the Number primitive value for a number object, simply use the

valueOf()

method:

var iNumber = oNumberObject.valueOf();

Of course, the

Number

class also has a

toString()

method, which was discussed at length in the section

on conversions. Aside from the standard methods inherited from the

Object

class, the

Number

class has

several methods specifically for working with number values.

Although you should understand that the

Boolean

object is available, it’s best to use

Boolean primitives only to avoid the problems mentioned in this section.

ECMAScript Basics

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