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Reference Types

Usage

Result

Number(false)

Number(true)

Number(undefined)

NaN

Number(null)

Number(“5.5”)

5.5

Number(“56”)

Number(“5.6.7”)

NaN

Number(new Object())

NaN

Number(100)

100

The last type cast,

String()

, is the simplest because it can accurately convert any value to a string

value. To execute the type cast, it simply calls the

toString()

method of the value that was passed in,

which converts 1 to “1”, true to “true”, false to “false”, and so on. The only difference between type cast-

ing as a string and using

toString()

is that the type cast can produce a string for a

null

undefined

value without error:

var s1 = String(null); //”null”

var oNull = null;

var s2 = oNull.toString(); //won’t work, causes an error

Type casting is very helpful when dealing with the loosely typed nature of ECMAScript, although you

should ensure that only proper values are used.

Reference Types

Reference types are commonly referred to as

classes

, which is to say that when you have a reference

value, you are dealing with an object. The vast number of predefined ECMAScript reference types are

discussed throughout the book. For now, the discussion focuses around the reference types that are

closely related to the primitive types just discussed.

ECMAScript doesn’t actually have classes in the traditional sense. In fact, the word “class” doesn’t

appear in ECMA-262 except to explain that there are no classes. ECMAScript defines “object defini-

tions” that are logically equivalent to classes in other programming languages. This book chooses to use

the term “class” because it is more familiar to most developers.

Objects are created by using the

new

operator and providing the name of the class to instantiate. For

example, this line creates an instance of the Object class:

var o = new Object();

ECMAScript Basics

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