From da78a9e329e272dedb2400b79a3bdeebff387d47 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:42:17 -0500 Subject: initial commit --- .../reference/global_objects/number/index.html | 188 +++++++++++++++++++++ 1 file changed, 188 insertions(+) create mode 100644 files/it/web/javascript/reference/global_objects/number/index.html (limited to 'files/it/web/javascript/reference/global_objects/number') diff --git a/files/it/web/javascript/reference/global_objects/number/index.html b/files/it/web/javascript/reference/global_objects/number/index.html new file mode 100644 index 0000000000..39c8eb37d2 --- /dev/null +++ b/files/it/web/javascript/reference/global_objects/number/index.html @@ -0,0 +1,188 @@ +--- +title: Number +slug: Web/JavaScript/Reference/Global_Objects/Number +translation_of: Web/JavaScript/Reference/Global_Objects/Number +--- +
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  1. {{JSRef}}
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Number is a primitive wrapper object used to represent and manipulate numbers like 37 or -9.25.
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The Number constructor contains constants and methods for working with numbers. Values of other types can be converted to numbers using the Number() function.

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The JavaScript Number type is a double-precision 64-bit binary format IEEE 754 value, like double in Java or C#. This means it can represent fractional values, but there are some limits to what it can store. A Number only keeps about 17 decimal places of precision; arithmetic is subject to rounding. The largest value a Number can hold is about 1.8×10308. Numbers beyond that are replaced with the special Number constant {{jsxref("Infinity")}}.

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A number literal like 37 in JavaScript code is a floating-point value, not an integer. There is no separate integer type in common everyday use. (JavaScript now has a {{jsxref("BigInt")}} type, but it was not designed to replace Number for everyday uses. 37 is still a Number, not a BigInt.)

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Description

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When used as a function, Number(value) converts a string or other value to the Number type. If the value can't be converted, it returns {{jsxref("NaN")}}.

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Literal syntax

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123    // one-hundred twenty-three
+123.0  // same
+123 === 123.0  // true
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Function syntax

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Number('123')  // returns the number 123
+Number('123') === 123  // true
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+Number("unicorn")  // NaN
+Number(undefined)  // NaN
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Constructor

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Number()
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Creates a new Number value.
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Static properties

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{{jsxref("Number.EPSILON")}}
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The smallest interval between two representable numbers.
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{{jsxref("Number.MAX_SAFE_INTEGER")}}
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The maximum safe integer in JavaScript (253 - 1).
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{{jsxref("Number.MAX_VALUE")}}
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The largest positive representable number.
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{{jsxref("Number.MIN_SAFE_INTEGER")}}
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The minimum safe integer in JavaScript (-(253 - 1)).
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{{jsxref("Number.MIN_VALUE")}}
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The smallest positive representable number—that is, the positive number closest to zero (without actually being zero).
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{{jsxref("Number.NaN")}}
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Special "Not a Number" value.
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{{jsxref("Number.NEGATIVE_INFINITY")}}
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Special value representing negative infinity. Returned on overflow.
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{{jsxref("Number.POSITIVE_INFINITY")}}
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Special value representing infinity. Returned on overflow.
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{{jsxref("Number.prototype")}}
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Allows the addition of properties to the Number object.
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Static methods

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{{jsxref("Number.isNaN()")}}
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Determine whether the passed value is NaN.
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{{jsxref("Number.isFinite()")}}
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Determine whether the passed value is a finite number.
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{{jsxref("Number.isInteger()")}}
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Determine whether the passed value is an integer.
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{{jsxref("Number.isSafeInteger()")}}
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Determine whether the passed value is a safe integer (number between -(253 - 1) and 253 - 1).
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{{jsxref("Number.parseFloat()", "Number.parseFloat(string)")}}
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This is the same as the global {{jsxref("parseFloat", "parseFloat()")}} function.
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{{jsxref("Number.parseInt()", "Number.parseInt(string, [radix])")}}
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This is the same as the global {{jsxref("parseInt", "parseInt()")}} function.
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Instance methods

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{{jsxref("Number.prototype.toExponential()" ,"Number.prototype.toExponential(fractionDigits)")}}
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Returns a string representing the number in exponential notation.
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{{jsxref("Number.prototype.toFixed()", "Number.prototype.toFixed(digits)")}}
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Returns a string representing the number in fixed-point notation.
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{{jsxref("Number.prototype.toLocaleString()", "Number.prototype.toLocaleString([locales [, options]])")}}
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Returns a string with a language sensitive representation of this number. Overrides the {{jsxref("Object.prototype.toLocaleString()")}} method.
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{{jsxref("Number.prototype.toPrecision()", "Number.prototype.toPrecision(precision)")}}
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Returns a string representing the number to a specified precision in fixed-point or exponential notation.
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{{jsxref("Number.prototype.toString()", "Number.prototype.toString([radix])")}}
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Returns a string representing the specified object in the specified radix ("base"). Overrides the {{jsxref("Object.prototype.toString()")}} method.
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{{jsxref("Number.prototype.valueOf()")}}
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Returns the primitive value of the specified object. Overrides the {{jsxref("Object.prototype.valueOf()")}} method.
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Examples

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Using the Number object to assign values to numeric variables

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

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const biggestNum     = Number.MAX_VALUE
+const smallestNum    = Number.MIN_VALUE
+const infiniteNum    = Number.POSITIVE_INFINITY
+const negInfiniteNum = Number.NEGATIVE_INFINITY
+const notANum        = Number.NaN
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Integer range for Number

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The following example shows the minimum and maximum integer values that can be represented as Number object. (More details on this are described in the ECMAScript standard, chapter 6.1.6 The Number Type.)

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const biggestInt  = Number.MAX_SAFE_INTEGER  //  (253 - 1) =>  9007199254740991
+const smallestInt = Number.MIN_SAFE_INTEGER  // -(253 - 1) => -9007199254740991
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When parsing data that has been serialized to JSON, integer values falling outside of this range can be expected to become corrupted when JSON parser coerces them to Number type.

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A possible workaround is to use {{jsxref("String")}} instead.

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Larger numbers can be represented using the {{jsxref("BigInt")}} type.

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Using Number to convert a Date object

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The following example converts the {{jsxref("Date")}} object to a numerical value using Number as a function:

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let d = new Date('December 17, 1995 03:24:00')
+console.log(Number(d))
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This logs 819199440000.

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Convert numeric strings and null to numbers

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Number('123')     // 123
+Number('123') === 123 /// true
+Number('12.3')    // 12.3
+Number('12.00')   // 12
+Number('123e-1')  // 12.3
+Number('')        // 0
+Number(null)      // 0
+Number('0x11')    // 17
+Number('0b11')    // 3
+Number('0o11')    // 9
+Number('foo')     // NaN
+Number('100a')    // NaN
+Number('-Infinity') //-Infinity
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Specifications

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Specification
{{SpecName('ESDraft', '#sec-number-objects', 'Number')}}
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Browser compatibility

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{{Compat("javascript.builtins.Number")}}

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See also

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