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JScript Data Type Conversion

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. A string delineated by single or double quotation marks; can contain zero or more unicode characters. An empty string ("") has zero characters and length.

·   Number. Can be an integer or floating point number 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 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

Input

 

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

runtime error

runtime error

New Boolean object

New Number object

New String object

no conversion

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