Difference between Primitive and non-primitive datatypes in JavaScript

I am not able to understand exactly what is difference between primitive and non primitive data types in JavaScript even it is declared using same name i.e var.

Data Types (JavaScript):

Primary Data Types
The primary (primitive) data types are:
String, Number, Boolean

Composite Data Types
The composite (reference) data types are:
Object, Array

Special Data Types
The special data types are:
Null, Undefined

Click here for details:

  var test1 = 1;
  var test2 = "Something";
  var test3 = true;
  var test4 = {};
  var test5 = new Array();
  var test6 = new Date();
  var test7;
  var test8 = null;

  alert(typeof (test1)); //number
  alert(typeof (test2)); //string
  alert(typeof (test3)); //boolean
  alert(typeof (test4)); //object
  alert(typeof (test5)); //object
  alert(typeof (test6)); //object
  alert(typeof (test7)); //undefined
  alert(typeof (test8)); //object