JavaScript Numbers

JavaScript has only one type of number.

Numbers can be written with, or without decimals.

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JavaScript Numbers

JavaScript numbers can be written with, or without decimals:

Example

var x = 3.14;    // A number with decimals
var y = 34;      // A number without decimals

Extra large or extra small numbers can be written with scientific (exponent) notation:

Example

var x = 123e5;    // 12300000
var y = 123e-5;   // 0.00123

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JavaScript Numbers are Always 64-bit Floating Point

Unlike many other programming languages, JavaScript does not define different types of numbers, like integers, short, long, floating-point etc.

JavaScript numbers are always stored as double precision floating point numbers, following the international IEEE 754 standard.

This format stores numbers in 64 bits, where the number (the fraction) is stored in bits 0 to 51, the exponent in bits 52 to 62, and the sign in bit 63:

Value (aka Fraction/Mantissa)	Exponent	Sign
52 bits (0 - 51)	11 bits (52 - 62)	1 bit (63)

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Precision

Integers (numbers without a period or exponent notation) are considered accurate up to 15 digits.

Example

var x = 999999999999999;   // x will be 999999999999999
var y = 9999999999999999;  // y will be 10000000000000000

Try it yourself »

The maximum number of decimals is 17, but floating point arithmetic is not always 100% accurate:

Example

var x = 0.2 + 0.1;         // x will be 0.30000000000000004

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To solve the problem above, it helps to multiply and divide:

Example

var x = (0.2 * 10 + 0.1 * 10) / 10;       // x will be 0.3

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Hexadecimal

JavaScript interprets numeric constants as hexadecimal if they are preceded by 0x.

Example

var x = 0xFF;             // x will be 255

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	Never write a number with a leading zero. Some JavaScript versions interprets numbers as octal if they are written with a leading zero.

By default, Javascript displays numbers as base 10 decimals.

But you can use the toString() method to output numbers as base 16 (hex), base 8 (octal), or base 2 (binary).

Example

var myNumber = 128;
myNumber.toString(16);     // returns 80
myNumber.toString(8);      // returns 200
myNumber.toString(2);      // returns 10000000

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Infinity

Infinity (or -Infinity) is the value JavaScript will return if you calculate a number outside the largest possible number.

Example

var myNumber = 2;
while (myNumber != Infinity) {          // Execute until Infinity
    myNumber = myNumber * myNumber;
}

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Division by 0 (zero) also generates Infinity:

Example

var x =  2 / 0;          // x will be Infinity
var y = -2 / 0;          // y will be -Infinity

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Infinity is a number: typeOf(Infinity) is a Number.

Example

typeof(Infinity);        // returns "number"

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NaN - Not a Number

NaN is a JavaScript reserved word indicating that a value is not a number.

You can use the global JavaScript function isNaN() to find out if a value is a number.

Example

var x = 100 / "Apple";  // a number divided by a string is not a number
var y = 100 / "10";     // a number divided by a numeric string is a number

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 Infinity is a number.

Example

isNaN(1000 / 0);        // returns false

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Watch out for NaN. If you use it in a mathematical operation, the result will also be NaN.

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Numbers Can be Numbers or Objects

JavaScript numbers can be primitive values created from literals, like var x = 123;

JavaScript number can also be objects created with the new keyword, like var y = new Number(123);

Example

var x = 123;
var y = new Number(123);
typeof(x);                 // returns number
typeof(y);                 // returns object

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	Don't use the new keyword. Number objects slow down execution speed, and produce nasty side effects:

Example

var x = 123;             
var y = new Number(123);
(x === y) // is false because x is a number and y is an object.

Try it yourself »

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Number Properties

• MAX_VALUE
• MIN_VALUE
• NEGATIVE_INFINITY
• POSITIVE_INFINITY
• NaN
• prototype
• constructor

Number properties belongs to JavaScript's number object wrapper called Number.

These properties can only be accessed as Number.MAX_VALUE.

Using num.MAX_VALUE, where num is a variable, expression, or value, will return undefined.

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Number Methods

• toExponential()
• toFixed()
• toPrecision()
• toString()
• valueOf()

Number methods can be used on any number, literal, variable, or expression:

Example

var x = 123;
x.valueOf();               // returns 123
(123).valueOf();           // returns 123
(100+23).valueOf();        // returns 123

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	Normally, primitive values (like 3.14) cannot have properties and methods (because they are not objects). However, JavaScript treats primitive values as objects when using properties and methods.

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Complete JavaScript Number Reference

For a complete reference, go to our Complete JavaScript Number Reference.

The reference contains descriptions and examples of all Number properties and methods.