JavaScript Numbers

Number Types

JavaScript has only one type of number.

Numbers can be written with or without decimals.

Example

let x = 3.14;    // A number with decimals

let y = 3;       // A number without decimals

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

Example

let x = 123e5;    // 12300000

let y = 123e-5;   // 0.00123

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:

Integer Precision

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

Example

let x = 999999999999999;   // x will be 999999999999999

let y = 9999999999999999;  // y will be 10000000000000000

The maximum number of decimals is 17.

Floating Precision

Example

let x = 0.2 + 0.1;

Example

let x = (0.2 * 10 + 0.1 * 10) / 10;

Adding Numbers and Strings

If you add two numbers, the result will be a number:

Example

let x = 10;

let y = 20;

let z = x + y;

If you add two strings, the result will be a string concatenation:

Example

let x = "10";

let y = "20";

let z = x + y;

If you add a number and a string, the result will be a string concatenation:

Example

let x = 10;

let y = "20";

let z = x + y;

If you add a string and a number, the result will be a string concatenation:

Example

let x = "10";

let y = 20;

let z = x + y;

A common mistake is to expect this result to be 30:

Example

let x = 10;

let y = 20;

let z = "The result is: " + x + y;

A common mistake is to expect this result to be 102030:

Example

let x = 10;

let y = 20;

let z = "30";

let result = x + y + z;

Numeric Strings

JavaScript strings can have numeric content:

Example

let x = 100;         // x is a number

let y = "100";       // y is a
string

JavaScript will try to convert strings to numbers in all numeric operations:

This will work:

Example

let x = "100";

let y = "10";

let z = x / y;

This will also work:

Example

let x = "100";

let y = "10";

let z = x * y;

And this will work:

Example

let x = "100";

let y = "10";

let z = x - y;

But this will not work:

Example

let x = "100";

let y = "10";

let z = x + y;

NaN - Not a Number

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

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

Example

let x = 100 / "Apple";

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

Example

let x = 100 / "10";

You can use the global JavaScript function isNaN() to find out if a value is a not a number:

Example

let x = 100 / "Apple";
isNaN(x);

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

Example

let x = NaN;

let y = 5;

let z = x + y;

Or the result might be a concatenation like NaN5:

Example

let x = NaN;

let y = "5";

let z = x + y;

NaN is a number: typeof NaN returns number:

Example

typeof NaN;

Infinity

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

Example

let myNumber = 2;

// Execute until Infinity

while (myNumber != Infinity) {

    myNumber = myNumber * myNumber;
}

Division by 0 (zero) also generates Infinity:

Example

let x =  2 / 0;

let y = -2 / 0;

Infinity is a number: typeof Infinity returns number.

Example

typeof Infinity;

Hexadecimal

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

Example

let x = 0xFF;

By default, JavaScript displays numbers as base 10 decimals.

But you can use the toString() method to output numbers from base 2 to base 36.

Hexadecimal is base 16. Decimal is base 10. Octal is base 8. Binary is base 2.

Example

let myNumber = 32;

myNumber.toString(32);

myNumber.toString(16);

myNumber.toString(12);

myNumber.toString(10);

myNumber.toString(8);

myNumber.toString(2);

JavaScript Numbers as Objects

Normally JavaScript numbers are primitive values created from literals:

Example

let x = 123;

But numbers can also be defined as objects with the keyword new:

Example

let y = new Number(123);

Example

let x = 123;

let y = new Number(123);

Example

let x = 500;

let y = new Number(500);

Example

let x = 500;

let y = new Number(500);

Example

let x = new Number(500);

let y = new Number(500);

Example

let x = new Number(500);

let y = new Number(500);