JavaScript Numbers

JavaScript has only one type of number. Numbers can be written with or without decimals.

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:

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.

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

The maximum number of decimals is 17.

Floating Precision

let x = 0.2 + 0.1;

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

Adding Numbers and Strings

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

let x = 10;
let y = 20;
let z = x + y;

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

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:

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:

let x = "10";
let y = 20;
let z = x + y;

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

let x = 10;
let y = 20;
let z = "The result is: " + x + y;

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

let x = 10;
let y = 20;
let z = "30";
let result = x + y + z;

Numeric Strings

JavaScript strings can have numeric content:

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:

let x = "100";
let y = "10";
let z = x / y;

This will also work:

let x = "100";
let y = "10";
let z = x * y;

And this will work:

let x = "100";
let y = "10";
let z = x - y;

But this will not work:

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):

let x = 100 / "Apple";

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

let x = 100 / "10";

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

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

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

let x = NaN;
let y = 5;
let z = x + y;

Or the result might be a concatenation like NaN5:

let x = NaN;
let y = "5";
let z = x + y;

NaN is a number: typeof NaN returns number:

typeof NaN;

Infinity

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

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

Division by 0 (zero) also generates Infinity:

let x =  2 / 0;
let y = -2 / 0;

Infinity is a number: typeof Infinity returns number.

typeof Infinity;

Hexadecimal

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

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.

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:

let x = 123;

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

let y = new Number(123);

let x = 123;
let y = new Number(123);

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

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

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

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