difference between pass by value and pass by reference in javascript code example

Example: javascript pass by value

function func(obj) {
  obj = JSON.parse(JSON.stringify(obj)); //If too slow, replace with other method of deep cloning
  obj.a += 10;
  return obj.a;
}

var myObj = {a: 5};
func(myObj); //Returns 15 and myObj.a is still 5