Javascript - Variable References Changing

What types of variables change like so?

var int1;
var int2;
var int3;


int1 = 42;
int2 = int3 = int1;
int1 += 3;

int1      // 45
int2      // 42
int3      // 42




arr1 = {};
arr2 = arr3 = arr1;
arr1.ab = 5; 

arr1      // Object {ab: 5}
arr2      // Object {ab: 5}
arr3      // Object {ab: 5}

Like howcome int2 and int3 changed and arr2 and arr3 didn't? What types change like this?

Answer

Primitive data types (number, string and boolean) do not change if you change a reference of it, whereas composite data types do change.

http://msdn.microsoft.com/en-us/library/ie/7wkd9z69(v=vs.94).aspx