JavaScript - Number

JavaScript has only one type of number. JavaScript numbers can be written with, or without decimals.

JavaScript numbers are always 64-bit floating point.

Infinity: Infinity (or -Infinity) is the value JavaScript will return if you calculate a number outside the largest possible number. Division by 0 (zero) also generates Infinity. Infinity is a number: typeOf Infinity returns number.

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

typeof Infinity; // returns "number"

NaN: NaN is a JavaScript reserved word indicating that a value is not a number. Trying to do arithmetic with a non-numeric string will result in NaN (Not a Number).

Numbers as 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).

Don't create Number objects. It slows down execution speed. Just remember, numbers as OBJECTS are not the same as Number Types (primitive data type).

var x = 500;
var y = new Number(500);
// (x == y) is true because x and y have equal VALUES
// (x === y) is false because x and y have different types

Misunderstanding Floats: All numbers in JavaScript are stored as 64-bits Floating point numbers (Floats). All programming languages, including JavaScript, have difficulties with precise floating point values.

var x = 0.1;
var y = 0.2;
var z = x + y       // the result in z will not be 0.3
if (z == 0.3)       // this if test will FAIL

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

var z = (x * 10 + y * 10) / 10;             // z will be 0.3
if (z == 0.3)                               // this if test will PASS