Javascript primitive data type

• Primitive types are:
  undefined
  null
  boolean
  number
  string

• undefined : when a variable is declared using var but not initialized.

  var nonInitializedVariable;

• null : Null is an empty object pointer
  var InitializedVariable = null;

• boolean : boolean literals are true and false and thy are case sensitive.

  var validBool = true; /// variable is defined and initialized        
  var nonValidBool = True; /// Error var True is not defined        

Falsy values:
false, "" empty string, 0, NaN, null, undefined

This is important while initializing varable eg:

  var someMessage = "this is example";    
if( someMessage ){   /// expresion is converted to true   }

• number : numbers using IEEE-754 format to represent both integers and floating-point values

  var myn = 9; /// integer
  
  var fl = 1.7; /// floating number

http://en.wikipedia.org/wiki/IEEE_floating_point

• string - string data type represents a sequence of zero or more 16-bit unicode characters. Strings can be delineated by either double quotes (“) or single quotes (‘).

  var oneQuote = 'this is valid string';    
  var twoQuote = "this is also valid string";