Description

Microsoft JScript provides automatic type conversion as the context may require. This means that if the context expects a value to be a string, for example, JScript tries to convert the value to a string.

The language has six types of data. All values have one of these types:

undefined

The undefined type has one value only, undefined.

Null

The null type has one value only, null.

Boolean

The Boolean type represents the two logical values, true and false.

String

Strings, delineated by single or double quotation marks, contain zero or more Unicode characters. An empty string ("") has zero characters and length.

Number

Numbers can be integers or floating-point numbers according to the IEEE 754 specification. There also several special values:

• NaN, or not a Number
• Positive Infinity
• Negative Infinity
• Positive zero
• Negative zero

Object

An Object type is an object definition including its set of properties and methods.

The following table defines what happens when the context requires that JScript convert one data type into another:

Output Data Type	Input Data Type
	Undefined	Null	Boolean	Number	String	Object
boolean	false	false	no conversion	false if +0, -0, or NaN; otherwise true	false if empty string (""); otherwise true	true
number	NaN	NaN	1 if true; +0 if false	no conversion	If it cannot be interpreted as a number, it is interpreted as NaN	Number object
string	"undefined"	"null"	"true" or "false"	The absolute value of the number plus its sign, with the following exceptions: NaN returns "NaN" +0 or -0 returns "0" + infinity returns "Infinity" - infinity returns "-Infinity"	no conversion	String object
object	run-time error	run-time error	New Boolean object	New Number object	New String object	no conversion