AJAX - The Complete Reference

PART IV

Appendix A: JavaScript Quick Reference 557

Type Conversion

Type conversion is automatically carried out in JavaScript. Table A-6 shows the common

conversion rules when data is automatically converted to one type or another. Automatic

conversion happens very often when using relational operators discussed later in the

section. It is also possible to force type conversion using a variety of built-in methods

summarized in Table A-7.

Value

Convert to

Boolean

Convert to

Number Convert to String Convert to Object

true 1 "true" Boolean object with

value of true

false 0 "false" Boolean object with

value of false

0 false "0" Number object with

value of 0

Any nonzero

number including

negative

numbers

true The number as

a string, so 40

becomes “40”

while −1.13

becomes "−1.13"

Number object of

the value indicated

Empty string "" false 0 String object with

no value

A nonempty

string

true

This means

that strings like

“0” and “false”

convert to true

as well.

If the string

contains solely

a number like

"4" it will be

converted into

the number. All

other strings will

be converted to

NaN. Note that

strings must

strictly contain

a number for

conversion for

example, "4no"

converts to NaN

and not 4.

String object

containing the string

primitive value

Any existing

object

true NaN Value of

toString()

method of the

object

null false 0 "null" TypeError Exception

thrown

undefined false NaN "undefined" TypeError Exception

thrown

TABLE A-6 Primitive JavaScript Data Types