Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

Availability

JavaScript 1.1; JScript 2.0; ECMAScript v1

Inherits from/Overrides

Inherits from Object

Constructor

new Number(value)
Number(value)

Arguments

value

The numeric value of the Number object being created, or a value to
be converted to a number.

Returns

When Number( ) is used with the
new operator as a constructor, it returns a newly
constructed Number object. When Number( ) is
invoked as a function without the new operator, it
converts its argument to a primitive numeric value and returns that
value (or NaN if the conversion failed).

Constants

Number.MAX_VALUE

The largest representable number.

Number.MIN_VALUE

The smallest representable number.

Number.NaN

Not-a-number value.

Number.NEGATIVE_INFINITY

Negative infinite value; returned on overflow.

Number.POSITIVE_INFINITY

Infinite value; returned on overflow.

Methods

toString( )

Converts a number to a string, using a specified radix (base).

toLocaleString( )

Converts a number to a string, using local number formatting
conventions.

toFixed( )

Converts a number to a string that contains a specified number of
digits after the decimal place.

toExponential( )

Converts a number to a string using exponential notation with the
specified number of digits after the decimal place.

toPrecision( )

Converts a number to a string using the specified number of
significant digits. Uses exponential or fixed-point notation
depending on the size of the number and the number of significant
digits specified.

Description

Numbers are a basic,
primitive
data type in JavaScript. In JavaScript 1.1, however, JavaScript also
supports the Number object, which is a wrapper object around a
primitive numeric value. JavaScript automatically converts between
the primitive and object forms as necessary. In JavaScript 1.1, you
can explicitly create a Number object with the Number(
) constructor, although there is rarely any need to do so.

The Number( ) constructor can also be used without
the new operator, as a conversion function. When
invoked in this way, it attempts to convert its argument to a number
and returns the primitive numeric value (or NaN) that results from
the conversion.

The Number( ) constructor is also used as a
placeholder for five useful numeric constants: the largest and
smallest representable numbers; positive and negative infinity; and
the special not-a-number value. Note that these values are properties
of the Number( ) constructor function itself, not
of individual number objects. For example, you can use the
MAX_VALUE property as follows:

var biggest = Number.MAX_VALUE

but

not like this:

var n = new Number(2);
var biggest = n.MAX_VALUE 

By contrast, the toString( ) and other methods of
the Number object are methods of each Number object, not of the
Number( ) constructor function. As noted earlier,
JavaScript automatically converts from primitive numeric values to
Number objects whenever necessary. This means that we can use the
Number methods with primitive numeric values as well as with Number
objects.

var value = 1234;
var binary_value = n.toString(2); 

See Also

Infinity, Math, NaN