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JavaScript Number : Object

constructor primitive

A numerical value. JavaScript stores numbers as 64 bit (8 byte) double precision floats. See Math for helpful math related functions. See also BigInt.

Spec

Number(value : BigInt) : Number

Converts the specified BigInt to a Number. For values outside the range MIN_SAFE_INTEGER to MAX_SAFE_INTEGER, the returned Number may be an approximation of value.

Example:

var x = Number(100n);
console.log(x);

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ECMAScript 2020 Spec

Number(value : Object) : Number

Coerces value to a number. Usually this method is not necessary since JavaScript will automatically coerce a value to a number when it is used in a number context. +value is another way to coerce a value to a number. This coercion is very strict and will return NaN if the specified value cannot be converted to a Number. parseInt and paseFloat can also be used to convert a String to a Number.

Example:

var one = '1';
console.log(one + 2); // 2 is converted to '2' and concatenated with '1'
console.log(Number(one) + 2); // convert '1' to a number first
console.log(+one + 2); // another way to convert to a number

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Spec

Constructors

new Number(value : Number) : Object

Creates a box for value.

Example:

var literal = 123;
var boxed = new Number(123);
literal.foo = "bar";
boxed.foo = "bar";
console.log(literal.foo);
console.log(boxed.foo);

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Spec

Instance Methods

toExponential([fractionalDigits : Number]) : String

Returns a string representation of this in scientific notation. If fractionalDigits is specified, that many digits will follow the '.'.

Example:

var x = 123.456;
console.log(x.toExponential());
console.log(x.toExponential(2));
console.log(x.toExponential(6));

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Spec

toFixed([fractionalDigits = 0 : Number]) : String

Returns a string representation of this with fractionalDigits following the '.'.

Example:

var x = 123.456;
console.log(x.toFixed());
console.log(x.toFixed(2));
console.log(x.toFixed(6));

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Spec

toLocaleString([locales : Array<String>, [options : Object]]) : String

options : {

currency	String
currencyDisplay	String
localeMatcher	String
maximumFractionDigits	Number
maximumSignificantDigits	Number
minimumFractionDigits	Number
minimumIntegerDigits	Number
minimumSignificantDigits	Number
style	String
useGrouping	Boolean

}

Returns a string representation of this that conforms to the number format specification of the current locale.

Example:

var x = 123.456;
console.log(x.toString());
console.log(x.toLocaleString());

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Spec

toPrecision(precision : Number) : String

Returns a string representation of this with precision significant digits.

Example:

var x = 123.456;
console.log(x.toPrecision(1));
console.log(x.toPrecision(2));
console.log(x.toPrecision(3));
console.log(x.toPrecision(4));

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Spec

toString([base = 10 : Number]) : String

Returns a string representation of this in the specified base. base must be an integer between 2 and 36.

Example:

var x = 0x123ABC;
console.log(x.toString());
console.log(x.toString(16));

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Spec

Number Properties

EPSILON : Number readonly

EPSILON is the difference between 1 and the next Number greater than 1 that is representable in JavaScript.

Example:

console.log(Number.EPSILON);
console.log(1 + Number.EPSILON);

// 1 plus a number smaller than EPSILON will either round
// to 1 or (1 + EPSILON)
var x = 1 + (Number.EPSILON * 0.8);
console.log(x);
console.log(x - 1);

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ECMAScript 2015 Spec

MAX_SAFE_INTEGER : Number readonly

The largest possible integer such that MAX_SAFE_INTEGER and MAX_SAFE_INTEGER + 1 can both be represented exactly in JavaScript. See also MIN_SAFE_INTEGER and Number.isSafeInteger().

Example:

console.log(Number.MAX_SAFE_INTEGER);
console.log(Number.MAX_SAFE_INTEGER + 1);
console.log(Number.MAX_SAFE_INTEGER + 2);

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ECMAScript 2015 Spec

MAX_VALUE : Number readonly

The largest possible Number less than infinity that can be represented in JavaScript.

Example:

console.log(Number.MAX_VALUE);

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Spec

MIN_SAFE_INTEGER : Number readonly

The smallest possible integer such that MIN_SAFE_INTEGER and MIN_SAFE_INTEGER - 1 can both be represented exactly in JavaScript. See also MAX_SAFE_INTEGER and Number.isSafeInteger().

Example:

console.log(Number.MIN_SAFE_INTEGER);
console.log(Number.MIN_SAFE_INTEGER - 1);
console.log(Number.MIN_SAFE_INTEGER - 2);

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ECMAScript 2015 Spec

MIN_VALUE : Number readonly

The smallest possible Number greater than 0 that can be represented in JavaScript.

Example:

console.log(Number.MIN_VALUE);

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Spec

NaN : Number readonly

Floating point Not a Number. Signifies an error in a calculation. NaN is never equal to another Number, even if it is NaN. To check if something is NaN, use isNan() or Number.isNan(). Also exists as NaN in the global namespace.

Example:

console.log(Number.NaN);
console.log(NaN);
console.log(0/0);
console.log(Math.sqrt(-1));

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Spec

NEGATIVE_INFINITIY : Number readonly

Negative infinity.

Example:

console.log(Number.NEGATIVE_INFINITY);
console.log(-Infinity);
console.log(-1/0);

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Spec

POSITIVE_INFINITIY : Number readonly

Positive infinity. Also exists as Infinity in the global namespace.

Example:

console.log(Number.POSITIVE_INFINITY);
console.log(Infinity);
console.log(1/0);

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Spec

Number Methods

isFinite(x : Number) : Boolean

Returns true if x is not NaN, +Infinity, or -Infinity. See also the global isFinite(x) method.

Example:

console.log(Number.isFinite(0/0)); // 0/0 is NaN
console.log(Number.isFinite(1/0)); // 1/0 is infinity
console.log(Number.isFinite(1.2)); // 1.2 is finite

console.log();

// Compare Number.isFinite and global isFinite methods
console.log(Number.isFinite('0')); // The string '0' is not a Number
console.log(isFinite('0')); // The string '0' is converted to a Number

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ECMAScript 2015 Spec

isInteger(x : Number) : Boolean

Returns true if x is an integer.

Example:

console.log(Number.isInteger(0)); 
console.log(Number.isInteger(1.0));
console.log(Number.isInteger(1.2));

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ECMAScript 2015 Spec

isNaN(x : Number) : Boolean

Returns true if x is NaN. NaN is never equal to another Number, even if it is NaN, so you must use isNaN to check for NaN. See also the global isNaN(x) method and Object.is().

Example:

var x = 0/0;
console.log(x === NaN); 
console.log(Number.isNaN(x));

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ECMAScript 2015 Spec

isSafeInteger(x : Number) : Boolean

Returns true if x is greater than or equal to MIN_SAFE_INTEGER and less than or equal to MAX_SAFE_INTEGER. Adding or subtracting 1 to numbers outside this range may not produce a change in the value due to lack of floating point precision.

Example:

console.log(Number.isInteger(42)); 
console.log(Number.isSafeInteger(Number.MAX_SAFE_INTEGER));
console.log(Number.isSafeInteger(Number.MAX_SAFE_INTEGER + 1));

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ECMAScript 2015 Spec

parseFloat(str : String) : Number

Converts str into a floating point number. parseFloat is less scrict than using Number(str) (or +str) to convert to a Number because it ignores extra characters after the numeric portion of the string. If the first character is not a valid number, parseFloat will return NaN. Also exists as parseFloat in the global namespace.

Example:

console.log(Number.parseFloat('12'));
console.log(Number.parseFloat('12.34'));
console.log(Number.parseFloat('0x12')); // Does not detect hex
console.log(Number.parseFloat('12e5')); // Supports scientific notation
console.log(Number.parseFloat('Infinity')); // Supports Infinity
console.log(Number.parseFloat === parseFloat); // Also available in the global namespace

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ECMAScript 2015 Spec

parseInt(str : String, [base : Number]) : Number

Converts str into an integral number. If base is not specified, parseInt will attempt to determine the base to use depending on the input ('0x' prefix is base 16). parseInt is less scrict than using Number(str) (or +str) to convert to a Number because it ignores extra characters after the numeric portion of the string. If the first character is not a valid number in the specified base, parseInt will return NaN. Also exists as parseInt in the global namespace.

Example:

console.log(Number.parseInt('12'));
console.log(Number.parseInt('12.34')); // Ignores non digits
console.log(Number.parseInt('0x12')); // Autodetects base 16
console.log(Number.parseInt('12', 16)); // Force base 16
console.log(Number.parseInt('12e5')); // Doesn't support scientific notation
console.log(Number.parseInt('Infinity')); // Doesn't support infinity
console.log(Number.parseInt == parseInt); // Also available in the global namespace

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ECMAScript 2015 Spec

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