实现一个继承

function Parent(name) {
  this.name = name;
}

Parent.prototype.sayName = function() {
  console.log("parent name:", this.name);
};

function Child(name, parentName) {
  Parent.call(this, parentName);
  this.name = name;
}

function create(proto) {
  function F() {}
  F.prototype = proto;
  return new F();
}
Child.prototype = create(Parent.prototype);
Child.prototype.sayName = function() {
  console.log("child name:", this.name);
};

Child.prototype.constructor = Child;
var parent = new Parent("汪某");
parent.sayName(); // parent name: 汪某
var child = new Child("son", "汪某");