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: http://www.arcetri.astro.it/irlab/doc/library/javascript/clientreference/number.htm
Дата изменения: Thu Oct 7 13:13:36 1999 Дата индексирования: Sat Dec 22 14:24:10 2007 Кодировка: Поисковые слова: observatory |
Number object is an object wrapper for primitive numeric values.
JavaScript 1.2: modified behavior of
JavaScript 1.3: added | |
Number constructor:
new Number(value)
value |
Number object are:
Number object.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 |
Description
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|
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| Special value representing negative infinity; returned on overflow.
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watch and unwatch methods from Object.
Number object's properties to assign values to several numeric variables:
biggestNum = Number.MAX_VALUEExample 2. The following example creates a
smallestNum = Number.MIN_VALUE
infiniteNum = Number.POSITIVE_INFINITY
negInfiniteNum = Number.NEGATIVE_INFINITY
notANum = Number.NaN
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"
Object.constructor.
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.
MAX_VALUE, the func1 function is called; otherwise, the func2 function is called.
if (num1 * num2 <= Number.MAX_VALUE)
func1()
else
func2()
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.
MIN_VALUE, the func1 function is called; otherwise, the func2 function is called.
if (num1 / num2 >= Number.MIN_VALUE)
func1()
else
func2()
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.
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.")
}
NaN, isNaN, parseFloat, parseInt
"-Infinity".POSITIVE_INFINITY, multiplied by NEGATIVE_INFINITY is NEGATIVE_INFINITY.
NEGATIVE_INFINITY, multiplied by NEGATIVE_INFINITY is POSITIVE_INFINITY.
NEGATIVE_INFINITY is NaN.
NaN multiplied by NEGATIVE_INFINITY is NaN.
NEGATIVE_INFINITY, divided by any negative value except NEGATIVE_INFINITY, is POSITIVE_INFINITY.
NEGATIVE_INFINITY, divided by any positive value except POSITIVE_INFINITY, is NEGATIVE_INFINITY.
NEGATIVE_INFINITY, divided by either NEGATIVE_INFINITY or POSITIVE_INFINITY, is NaN.
NEGATIVE_INFINITY is Zero.
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.
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()
Infinity, isFinite
"Infinity".POSITIVE_INFINITY, multiplied by POSITIVE_INFINITY is POSITIVE_INFINITY.
NEGATIVE_INFINITY, multiplied by POSITIVE_INFINITY is NEGATIVE_INFINITY.
POSITIVE_INFINITY is NaN.
NaN multiplied by POSITIVE_INFINITY is NaN.
POSITIVE_INFINITY, divided by any negative value except NEGATIVE_INFINITY, is NEGATIVE_INFINITY.
POSITIVE_INFINITY, divided by any positive value except POSITIVE_INFINITY, is POSITIVE_INFINITY.
POSITIVE_INFINITY, divided by either NEGATIVE_INFINITY or POSITIVE_INFINITY, is NaN.
POSITIVE_INFINITY is Zero.
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.
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()
Infinity, isFinite
Function.prototype.toSource()
toSource method returns the following values:
function Number() {
[native code]
}Number, toSource returns a string representing the source code.
Object.toSource
toString()
toString([radix])
radix | An integer between 2 and 36 specifying the base to use for representing numeric values. |
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()
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.
x = new Number();
alert(x.valueOf()) //displays 0
Object.valueOf
Last Updated: 05/28/99 12:00:02