JavaScript numbers are always stored as double-precision 64-bit binary format IEEE 754. 
This format stores numbers in 64 bits, 

• 0-51 bit stores value(fraction)
• 52-62 bit stores exponent
• 63-bit stores sign

The types of number literals You can use decimal, binary, octal, and hexadecimal.

• Decimal Numbers: 
  JavaScript Numbers does not have different types of numbers(ex: int, float, long, short) which other programming languages do. It has only one type of number and it can hold both with or without decimal values.

Var a=33;
var b=3.3;
var x = 0562   //x will be 370(parsed as an octal number).

• If the number starts with 0 and the following number is smaller than 8. It will be parsed as an Octal Number.
  Integers are accurate up to 15 digits: 

var a = 999999999999999;   // a will be 999999999999999
var b = 9999999999999999;     // b will be 10000000000000000

• The floating point is not 100% accurate. The maximum number of decimals is up to 17.

var x = 0.22 + 0.12;   //x will be 0.33999999999999997

• Example-1: 

• Output: 
   

• Binary Numbers 
  They start with 0b or 0B followed by 0’s and 1’s. 
   

var x = 0b11;        // x will be 3
var x = 0B0111;       // x will be 7

• Example-2: 

• Output: 
   

• Octal Numbers 
  They start with 0 followed by a number of ranges from 0-7. If any number is used it will be taken as a decimal number. 

var x = 0111;      //x will be 73
var x = 07123;     //x will be 3667

• Example-3: 

• Output: 
   

• Hexadecimal Numbers 
  They start with 0x or 0X followed by any digit belonging (0123456789ABCDEF) 

var x = 0xfff;         //x will be 4095

• Example-2: 

• Output: 

• Exponentiation: 

var x = 2E5   // x will be 200000
var x = 34e3   // x will be 34000
var x = 23e-5 //x will be 0.00023

• JavaScript uses the + operator for both addition and concatenation. 
  • Addition: 

var a = 20;
var b = 20;
var c = a + b;           // c will be 40 (a number)

• Concatenation: 

var a = "10";
var b = "20";
var c = a + b;           // c will be 1020 (a string)

• Numeric Strings 
  NaN is a reserved word indicating not a number.

 var x= "12345" ;        // x will be a string(NaN)   
 var x = 67 ;            // x will be number