<script>
function Cat(name, color) {
  this.name = name;
  this.color = color;
  this.type = "猫科动物";
  this.eat = function () {
    alert("吃老鼠");
  };
  }


//生成实例：
var cat1 = new Cat("大毛", "黄色");
var cat2 = new Cat("二毛", "黑色");
alert(cat1.type);     // 猫科动物
cat1.eat();    // 吃老鼠 

alert(cat1.eat == cat2.eat); //false
</script>

<script>
function Cat(name, color) {
  this.name = name;
  this.color = color;
  }


Cat.prototype.type = "猫科动物";
Cat.prototype.eat = function () {
  alert("吃老鼠")
};


//生成实例。
var cat1 = new Cat("大毛", "黄色");
var cat2 = new Cat("二毛", "黑色");
alert(cat1.type); // 猫科动物
cat1.eat();// 吃老鼠


alert(cat1.eat == cat2.eat);//trueF
</script>