THE WORLD'S LARGEST WEB DEVELOPER SITE
×

JS Tutorial

JS HOME JS Introduction JS Where To JS Output JS Syntax JS Statements JS Comments JS Variables JS Operators JS Arithmetic JS Assignment JS Data Types JS Functions JS Objects JS Scope JS Events JS Strings JS String Methods JS Numbers JS Number Methods JS Math JS Random JS Dates JS Date Formats JS Date Methods JS Arrays JS Array Methods JS Array Sort JS Booleans JS Comparisons JS Conditions JS Switch JS Loop For JS Loop While JS Break JS Type Conversion JS Bitwise JS RegExp JS Errors JS Debugging JS Hoisting JS Strict Mode JS Style Guide JS Best Practices JS Mistakes JS Performance JS Reserved Words JS Versions JS JSON

JS Forms

JS Forms Forms API

JS Objects

Object Definitions Object Properties Object Methods Object Prototypes

JS Functions

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

JS HTML DOM

DOM Intro DOM Methods DOM Document DOM Elements DOM HTML 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 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 Objects JSON Arrays JSON Parse JSON Stringify JSON PHP JSON HTML JSON JSONP

JS Examples

JS Examples JS HTML DOM JS HTML Input JS HTML Objects JS HTML Events JS Browser 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

var x = 3.14;    // A number with decimals
var y = 3;       // A number without decimals

Try it yourself »

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

Example

var x = 123e5;    // 12300000
var 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

var x = 999999999999999;   // x will be 999999999999999
var 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

var 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

var 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

var x = 10;
var y = 20;
var 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

var x = "10";
var y = "20";
var 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

var x = 10;
var y = "20";
var 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

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

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

Example

var x = 10;
var y = 20;
var z = "The result is: " + x + y;
Try it Yourself »

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

Example

var x = 10;
var y = 20;
var z = "30";
var result = x + y + z;
Try it Yourself »

The JavaScript compiler 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:

var x = 100;         // x is a number

var y = "100";       // y is a string

JavaScript will try to convert strings to numbers in all numeric operations:

This will work:

var x = "100";
var y = "10";
var z = x / y;       // z will be 10

Try it Yourself »

This will also work:

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

Try it Yourself »

And this will work:

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

Try it Yourself »

But this will not work:

var x = "100";
var y = "10";
var 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

var 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

var 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

var 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

var x = NaN;
var y = 5;
var z = x + y;         // z will be NaN
Try it Yourself »

Or the result might be a concatenation:

Example

var x = NaN;
var y = "5";
var 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

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

Division by 0 (zero) also generates Infinity:

Example

var x =  2 / 0;          // x will be Infinity
var 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

var 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 as base 16 (hex), base 8 (octal), or base 2 (binary).

Example

var myNumber = 128;
myNumber.toString(16);  // returns 80
myNumber.toString(8);   // returns 200
myNumber.toString(2);   // returns 10000000
Try it Yourself »

Numbers Can be Objects

Normally JavaScript numbers are primitive values created from literals:

var x = 123;

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

var y = new Number(123);

Example

var x = 123;
var 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

var x = 500;             
var 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

var x = 500;             
var 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

var x = new Number(500);             
var 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.


Test Yourself with Exercises!

Exercise 1 »   Exercise 2 »   Exercise 3 »   Exercise 4 »