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:

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

Floating point arithmetic is not always 100% accurate:

let x = 0.2 + 0.1;

 

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

let x = (0.2 * 10 + 0.1 * 10) / 10;

 

Adding Numbers and Strings

WARNING !!

JavaScript uses the + operator for both addition and concatenation.

Numbers are added. Strings are concatenated.

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;

 

The JavaScript interpreter works from left to right.

First 10 + 20 is added because x and y are both numbers.

Then 30 + "30" is concatenated because z is a string.

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;

 

In the last example JavaScript uses the + operator to concatenate the strings.

NaN - Not a Number

NaN is a JavaScript reserved word indicating that a n