Tutorials References Exercises Videos Pro NEW Menu
Paid Courses Website NEW

JS Tutorial

JS HOME JS Introduction JS Where To JS Output JS Statements JS Syntax JS Comments JS Variables JS Let JS Const JS Operators JS Arithmetic JS Assignment JS Data Types JS Functions JS Objects JS Events JS Strings JS String Methods JS String Search JS String Templates JS Numbers JS Number Methods JS Arrays JS Array Methods JS Array Sort JS Array Iteration JS Array Const JS Dates JS Date Formats JS Date Get Methods JS Date Set Methods JS Math JS Random JS Booleans JS Comparisons JS If Else JS Switch JS Loop For JS Loop For In JS Loop For Of JS Loop While JS Break JS Iterables JS Sets JS Maps JS Typeof JS Type Conversion JS Bitwise JS RegExp JS Errors JS Scope JS Hoisting JS Strict Mode JS this Keyword JS Arrow Function JS Classes JS Modules JS JSON JS Debugging JS Style Guide JS Best Practices JS Mistakes JS Performance JS Reserved Words

JS Versions

JS Versions JS 2009 (ES5) JS 2015 (ES6) JS 2016 JS 2017 JS 2018 JS IE / Edge JS History

JS Objects

Object Definitions Object Properties Object Methods Object Display Object Accessors Object Constructors Object Prototypes Object Iterables Object Sets Object Maps Object Reference

JS Functions

Function Definitions Function Parameters Function Invocation Function Call Function Apply Function Bind Function Closures

JS Classes

Class Intro Class Inheritance Class Static

JS Async

JS Callbacks JS Asynchronous JS Promises JS Async/Await

JS HTML DOM

DOM Intro DOM Methods DOM Document DOM Elements DOM HTML DOM Forms DOM CSS DOM Animations DOM Events DOM Event Listener DOM Navigation DOM Nodes DOM Collections DOM Node Lists

JS Browser BOM

JS Window JS Screen JS Location JS History JS Navigator JS Popup Alert JS Timing JS Cookies

JS Web APIs

Web API Intro Web Forms API Web History API Web Storage API Web Worker API Web Fetch API Web Geolocation API

JS AJAX

AJAX Intro AJAX XMLHttp AJAX Request AJAX Response AJAX XML File AJAX PHP AJAX ASP AJAX Database AJAX Applications AJAX Examples

JS JSON

JSON Intro JSON Syntax JSON vs XML JSON Data Types JSON Parse JSON Stringify JSON Objects JSON Arrays JSON Server JSON PHP JSON HTML JSON JSONP

JS vs jQuery

jQuery Selectors jQuery HTML jQuery CSS jQuery DOM

JS Graphics

JS Graphics JS Canvas JS Plotly JS Chart.js JS Google Chart JS D3.js

JS Examples

JS Examples JS HTML DOM JS HTML Input JS HTML Objects JS HTML Events JS Browser JS Editor JS Exercises JS Quiz JS Certificate

JS References

JavaScript Objects HTML DOM Objects


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)

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
Try it Yourself »

The maximum number of decimals is 17.

Floating Precision

Floating point arithmetic is not always 100% accurate:

let x = 0.2 + 0.1;

Try it Yourself »

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

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

Try it Yourself »

This will also work:

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

Try it Yourself »

And this will work:

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

Try it Yourself »

But this will not work:

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

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";

Try it Yourself »

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

Example

let x = 100 / "10";
Try it Yourself »

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);
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;
Try it Yourself »

Or the result might be a concatenation like NaN5:

Example

let x = NaN;
let y = "5";
let z = x + y;
Try it Yourself »

NaN is a number: typeof NaN returns number:

Example

typeof NaN;
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;
// Execute until Infinity
while (myNumber != Infinity) {
  myNumber = myNumber * myNumber;
}
Try it Yourself »

Division by 0 (zero) also generates Infinity:

Example

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

Infinity is a number: typeof Infinity returns number.

Example

typeof Infinity;
Try it Yourself »

Hexadecimal

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

Example

let x = 0xFF;
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(32);
myNumber.toString(16);
myNumber.toString(12);
myNumber.toString(10);
myNumber.toString(8);
myNumber.toString(2);
Try it Yourself »

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);
Try it Yourself »

Do not create Number objects.

The new keyword complicates the code and slows down execution speed.

Number Objects can produce unexpected results:

When using the == operator, x and y are equal:

let x = 500;
let y = new Number(500);
Try it Yourself »

When using the === operator, x and y are not equal.

let x = 500;
let y = new Number(500);
Try it Yourself »

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

(x == y) true or false?

let x = new Number(500);
let y = new Number(500);
Try it Yourself »

(x === y) true or false?

let x = new Number(500);
let y = new Number(500);
Try it Yourself »

Comparing two JavaScript objects always returns false.

Complete JavaScript Number Reference

For a complete Number reference, visit our:

Complete JavaScript Number Reference.

The reference contains descriptions and examples of all Number properties and methods.