Core JavaScript 1.5 Reference:Global Objects:Number

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目录 1 摘要 2 Created by 3 Parameters 4 Description 5 Properties 6 Methods 7 Examples 7.1 Example: Using the Number object to assign values to numeric variables 7.2 Example: Using Number object to modify all Number objects

[编辑] 摘要

核心对象

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

[编辑] Created by

Number对象构造器

new Number(value)

[编辑] Parameters

value 

The numeric value of the object being created.

[编辑] Description

The primary uses for the Number object are:

• To access its constant properties, which represent the largest and smallest representable numbers, positive and negative infinity, and the Not-a-Number value.

• To create numeric objects that you can add properties to. Most likely, you will rarely need to create a Number object.

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, the following prints NaN:

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

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

[编辑] Properties

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.

[编辑] Methods

toExponential: Returns a string representing the number in exponential notation.

toFixed: Returns a string representing the number in fixed-point notation.

toLocaleString: Returns a human readable string representing the number using the locale of the environment. Overrides the Object.toLocaleString method.

toPrecision: Returns a string representing the number to a specified precision in fixed-point or exponential notation.

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.

[编辑] Examples

[编辑] Example: Using the Number object to assign values to numeric variables

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;

[编辑] Example: Using Number object to modify all Number objects

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";