<script type="text/javascript">
  function Person(){
    }
    Person.prototype.name = "allen";

    var person = new Person();
    console.log(person.hasOwnProperty("name")); //false
    console.log("name" in person); //true
    console.log(person.name); //"allen"

    person.name = "justforse";
    console.log(person.hasOwnProperty("name")); //true
    console.log("name" in person); //true
    console.log(person.name); //"justforuse"

    delete person.name;
    console.log(person.hasOwnProperty("name")); //false
    console.log("name" in person); //true
    console.log(person.name); //"allen"
</script>