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 = 34.00;    // 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

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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 (like 07). Some JavaScript versions interpret 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 returns 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.

Trying to do arithmetic with a non-numeric string will result in NaN (Not a Number):

Example

var x = 100 / "Apple";  // x will be NaN (Not a Number)

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However, if the string contains a numeric value , the result will be a number:

Example

var x = 100 / "10";     // x will be 10

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

Example

var x = 100 / "Apple";
isNaN(x);               // returns true because x is Not a Number

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

Example

var x = NaN;
var y = 5;
var z = x + y;         // z will be NaN

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 Or the result might be a concatenation:

Example

var x = NaN;
var y = "5";
var z = x + y;         // z will be NaN5

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NaN is a number, and typeof NaN returns number:

Example

typeof NaN;             // returns "number"

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Numbers Can be Objects

Normally JavaScript numbers are primitive values created from literals: var x = 123

But numbers can also be defined as objects with the keyword new: 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 create Number objects. They slow down execution speed, and produce nasty side effects:

When using the == equality operator, equal numbers looks equal:

Example

var x = 500;            
var y = new Number(500);

// (x == y) is true because x and y have equal values

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When using the === equality operator, equal numbers are not equal, because the === operator expects equality in both type and value.

Example

var x = 500;            
var y = new Number(500);

// (x === y) is false because x and y have different types

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Or even worse. Objects cannot be compared:

Example

var x = new Number(500);            
var y = new Number(500);

// (x == y) is false because objects cannot be compared

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	JavaScript objects cannot be compared.

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Number Properties and Methods

Primitive values (like 3.14 or 2014), cannot have properties and methods (because they are not objects).

But with JavaScript, methods and properties are also available to primitive values, because JavaScript treats primitive values as objects when executing methods and properties.

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Number Properties

Property	Description
MAX_VALUE	Returns the largest number possible in JavaScript
MIN_VALUE	Returns the smallest number possible in JavaScript
NEGATIVE_INFINITY	Represents negative infinity (returned on overflow)
NaN	Represents a "Not-a-Number" value
POSITIVE_INFINITY	Represents infinity (returned on overflow)

Example

var x = Number.MAX_VALUE;

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

These properties can only be accessed as Number.MAX_VALUE.

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

Example

var x = 6;
var y = x.MAX_VALUE;    // y becomes undefined