JS 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:

Note: Most programming languages have many number types: Whole numbers (integers): byte (8-bit), short (16-bit), int (32-bit), long (64-bit) Real numbers (floating-point): float (32-bit), double (64-bit). Javascript numbers are always double (64-bit floating point).

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

let x = 0.2 + 0.1;

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;

Note: 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;

Note: 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 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;

Note: 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 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:

let x = 123;

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

let y = new Number(123);

Example

let x = 123;

let y = new Number(123);

Note: Do not create Number objects. The new keyword complicates the code and slows down execution speed. Number Objects can produce unexpected results:

let x = 500;

let y = new Number(500);

let x = 500;

let y = new Number(500);

Note: the difference between (x==y) and (x===y).

let x = new Number(500);

let y = new Number(500);

let x = new Number(500);

let y = new Number(500);

Note: Comparing two JavaScript objects always returns false.

Note: Learn More: JavaScript Number Methods JavaScript Number Properties JavaScript Number Reference