Полезная информация

Table of Contents | Previous | Next | Index


Number

Lets you work with numeric values. The Number object is an object wrapper for primitive numeric values.

Core object

Implemented in

JavaScript 1.1, NES 2.0

JavaScript 1.2: modified behavior of Number constructor

JavaScript 1.3: added toSource method

ECMA version

ECMA-262

Created by

The Number constructor:

new Number(value)

Parameters

value

The numeric value of the object being created.

Description

The primary uses for the Number object are:

The properties of Number are properties of the class itself, not of individual Number objects.

JavaScript 1.2: Number(x) now produces NaN rather than an error if x is a string that does not contain a well-formed numeric literal. For example,

x=Number("three");
document.write(x + "<BR>");
prints NaN

You can convert any object to a number using the top-level Number function.

Property Summary

Property Description
constructor

Specifies the function that creates an object's prototype.

MAX_VALUE

The largest representable number.

MIN_VALUE

The smallest representable number.

NaN

Special "not a number" value.

NEGATIVE_INFINITY

Special value representing negative infinity; returned on overflow.

POSITIVE_INFINITY

Special value representing infinity; returned on overflow.

prototype

Allows the addition of properties to a Number object.

Method Summary

Method Description
toSource

Returns an object literal representing the specified Number object; you can use this value to create a new object. Overrides the Object.toSource method.

toString

Returns a string representing the specified object. Overrides the Object.toString method.

valueOf

Returns the primitive value of the specified object. Overrides the Object.valueOf method.

In addition, this object inherits the watch and unwatch methods from Object.

Examples

Example 1. The following example uses the Number object's properties to assign values to several numeric variables:

biggestNum = Number.MAX_VALUE
smallestNum = Number.MIN_VALUE
infiniteNum = Number.POSITIVE_INFINITY
negInfiniteNum = Number.NEGATIVE_INFINITY
notANum = Number.NaN
Example 2. The following example creates a Number object, myNum, then adds a description property to all Number objects. Then a value is assigned to the myNum object's description property.

myNum = new Number(65)
Number.prototype.description=null
myNum.description="wind speed"

constructor

Specifies the function that creates an object's prototype. Note that the value of this property is a reference to the function itself, not a string containing the function's name.

Property of

Number

Implemented in

JavaScript 1.1, NES 2.0

ECMA version

ECMA-262

Description

See Object.constructor.


MAX_VALUE

The maximum numeric value representable in JavaScript.

Property of

Number

Static, Read-only

Implemented in

JavaScript 1.1, NES 2.0

ECMA version

ECMA-262

Description

The MAX_VALUE property has a value of approximately 1.79E+308. Values larger than MAX_VALUE are represented as "Infinity".

Because MAX_VALUE is a static property of Number, you always use it as Number.MAX_VALUE, rather than as a property of a Number object you created.

Examples

The following code multiplies two numeric values. If the result is less than or equal to MAX_VALUE, the func1 function is called; otherwise, the func2 function is called.

if (num1 * num2 <= Number.MAX_VALUE)
   func1()
else
   func2()

MIN_VALUE

The smallest positive numeric value representable in JavaScript.

Property of

Number

Static, Read-only

Implemented in

JavaScript 1.1, NES 2.0

ECMA version

ECMA-262

Description

The MIN_VALUE property is the number closest to 0, not the most negative number, that JavaScript can represent.

MIN_VALUE has a value of approximately 5e-324. Values smaller than MIN_VALUE ("underflow values") are converted to 0.

Because MIN_VALUE is a static property of Number, you always use it as Number.MIN_VALUE, rather than as a property of a Number object you created.

Examples

The following code divides two numeric values. If the result is greater than or equal to MIN_VALUE, the func1 function is called; otherwise, the func2 function is called.

if (num1 / num2 >= Number.MIN_VALUE)
   func1()
else
   func2()

NaN

A special value representing Not-A-Number. This value is represented as the unquoted literal NaN.

Property of

Number

Read-only

Implemented in

JavaScript 1.1, NES 2.0

ECMA version

ECMA-262

Description

JavaScript prints the value Number.NaN as NaN.

NaN is always unequal to any other number, including NaN itself; you cannot check for the not-a-number value by comparing to Number.NaN. Use the isNaN function instead.

You might use the NaN property to indicate an error condition for a function that should return a valid number.

Examples

In the following example, if month has a value greater than 12, it is assigned NaN, and a message is displayed indicating valid values.

var month = 13
if (month < 1 || month > 12) {
   month = Number.NaN
   alert("Month must be between 1 and 12.")
}

See also

NaN, isNaN, parseFloat, parseInt


NEGATIVE_INFINITY

A special numeric value representing negative infinity. This value is represented as the unquoted literal "-Infinity".

Property of

Number

Static, Read-only

Implemented in

JavaScript 1.1, NES 2.0

ECMA version

ECMA-262

Description

This value behaves slightly differently than mathematical infinity:

Because NEGATIVE_INFINITY is a static property of Number, you always use it as Number.NEGATIVE_INFINITY, rather than as a property of a Number object you created.

Examples

In the following example, the variable smallNumber is assigned a value that is smaller than the minimum value. When the if statement executes, smallNumber has the value "-Infinity", so the func1 function is called.

var smallNumber = -Number.MAX_VALUE*10
if (smallNumber == Number.NEGATIVE_INFINITY)
   func1()
else
   func2()

See also

Infinity, isFinite


POSITIVE_INFINITY

A special numeric value representing infinity. This value is represented as the unquoted literal "Infinity".

Property of

Number

Static, Read-only

Implemented in

JavaScript 1.1, NES 2.0

ECMA version

ECMA-262

Description

This value behaves slightly differently than mathematical infinity:

Because POSITIVE_INFINITY is a static property of Number, you always use it as Number.POSITIVE_INFINITY, rather than as a property of a Number object you created.

Examples

In the following example, the variable bigNumber is assigned a value that is larger than the maximum value. When the if statement executes, bigNumber has the value "Infinity", so the func1 function is called.

var bigNumber = Number.MAX_VALUE * 10
if (bigNumber == Number.POSITIVE_INFINITY)
   func1()
else
   func2()

See also

Infinity, isFinite


prototype

Represents the prototype for this class. You can use the prototype to add properties or methods to all instances of a class. For information on prototypes, see Function.prototype.

Property of

Number

Implemented in

JavaScript 1.1, NES 2.0

ECMA version

ECMA-262


toSource

Returns a string representing the source code of the object.

Method of

Number

Implemented in

JavaScript 1.3

Syntax

toSource()

Parameters

None

Description

The toSource method returns the following values:

This method is usually called internally by JavaScript and not explicitly in code.

See also

Object.toSource


toString

Returns a string representing the specified Number object.

Method of

Number

Implemented in

JavaScript 1.1

ECMA version

ECMA-262

Syntax

toString()
toString(radix)

Parameters

radix

(Optional) An integer between 2 and 36 specifying the base to use for representing numeric values.

Description

The Number object overrides the toString method of the Object object; it does not inherit Object.toString. For Number objects, the toString method returns a string representation of the object.

JavaScript calls the toString method automatically when a number is to be represented as a text value or when a number is referred to in a string concatenation.

For Number objects and values, the built-in toString method returns the string representing the value of the number.

You can use toString on numeric values, but not on numeric literals:

// The next two lines are valid
var howMany=10
alert("howMany.toString() is " + howMany.toString())
// The next line causes an error
alert("45.toString() is " + 45.toString())

valueOf

Returns the primitive value of a Number object.

Method of

Number

Implemented in

JavaScript 1.1

ECMA version

ECMA-262

Syntax

valueOf()

Parameters

None

Description

The valueOf method of Number returns the primitive value of a Number object as a number data type.

This method is usually called internally by JavaScript and not explicitly in code.

Examples

x = new Number();
alert(x.valueOf())      //displays 0

See also

Object.valueOf


Table of Contents | Previous | Next | Index

Last Updated: 11/16/98 12:56:57

Copyright ╘ 1998 Netscape Communications Corporation