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JavaScript Numbers


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

Try it yourself »

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

Example

let x = 123e5;    // 12300000
let y = 123e-5;   // 0.00123

Try it yourself »


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)

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
Try it Yourself »

The maximum number of decimals is 17, but floating point arithmetic is not always 100% accurate:

Example

let x = 0.2 + 0.1;         // x will be 0.30000000000000004

Try it yourself »

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

Example

let x = (0.2 * 10 + 0.1 * 10) / 10;       // x will be 0.3
Try it Yourself »


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;           // z will be 30 (a number)
Try it Yourself »

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

Example

let x = "10";
let y = "20";
let z = x + y;           // z will be 1020 (a string)
Try it Yourself »

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;           // z will be 1020 (a string)
Try it Yourself »

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;           // z will be 1020 (a string)
Try it Yourself »

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;
Try it Yourself »

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;
Try it Yourself »

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;       // z will be 10

Try it Yourself »

This will also work:

let x = "100";
let y = "10";
let z = x * y;       // z will be 1000

Try it Yourself »

And this will work:

let x = "100";
let y = "10";
let z = x - y;       // z will be 90

Try it Yourself »

But this will not work:

let x = "100";
let y = "10";
let z = x + y;       // z will not be 110 (It will be 10010)

Try it Yourself »

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";  // x will be NaN (Not a Number)

Try it Yourself »

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

Example

let x = 100 / "10";     // x will be 10
Try it Yourself »

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

Example

let x = 100 / "Apple";
isNaN(x);               // returns true because x is Not a Number
Try it Yourself »

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;         // z will be NaN
Try it Yourself »

Or the result might be a concatenation:

Example

let x = NaN;
let y = "5";
let z = x + y;         // z will be NaN5
Try it Yourself »

NaN is a number: typeof NaN returns number:

Example

typeof NaN;            // returns "number"
Try it Yourself »

Infinity

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

Example

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

Division by 0 (zero) also generates Infinity:

Example

let x =  2 / 0;       // x will be Infinity
let y = -2 / 0;       // y will be -Infinity
Try it Yourself »

Infinity is a number: typeof Infinity returns number.

Example

typeof Infinity;     // returns "number"
Try it Yourself »

Hexadecimal

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

Example

let x = 0xFF;        // x will be 255
Try it Yourself »

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(10);  // returns 32
myNumber.toString(32);  // returns 10
myNumber.toString(16);  // returns 20
myNumber.toString(8);   // returns 40
myNumber.toString(2);   // returns 100000
Try it Yourself »

Numbers Can be 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);

// typeof x returns number
// typeof y returns object
Try it yourself »

Do not create Number objects. It slows down execution speed.
The new keyword complicates the code. This can produce some unexpected results:

When using the == operator, equal numbers are equal:

Example

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

// (x == y) is true because x and y have equal values
Try it Yourself »

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

Example

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

// (x === y) is false because x and y have different types
Try it Yourself »

Or even worse. Objects cannot be compared:

Example

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

// (x == y) is false because objects cannot be compared
Try it Yourself »

Note the difference between (x==y) and (x===y).
Comparing two JavaScript objects will always return false.