function addTen(num) {
  num = num + 10;
  return num;
}

var count = 20;
var result = addTen(count);
alert(count);   //20
alert(result);   //30

function setName (obj) {
   obj.name = "Nicolas";
}

var person = new Object();
setName(person);
alert(person.name);  //"Nicolas"  看起来像按引用传递，但是↓

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function setName (obj) {
   obj.name = "Nicolas";
   obj =new Object();
   obj.name = "Greg";
}

var person = new Object();
setName(person);
alert(person.name);   //如果是按引用传递，这里应该输出是“Greg”，但是输出结果是“Nicolas”
”