1.js原型
java有class和instance，js只有构造函数（function Cat(name,age){this.name=name;this.age=age}）,为了实现数据共享和抽象出通用的属性，加了一个原型prototype
eg:
function Cat(name,age){
this.name = name;//这里的this相当于java里面的instance
this.age = age;
this.work = function(){
alert("I am working");
}
}
var cat1 = new Cat("cat1",13);
var cat2 = new Cat("cat2",15);
cat1和cat2的都有work属性，但是一样的属性，明显是多余的，造成浪费，可以抽象出原型出来
function Dog(name,age){
this.name = name;
this.age = age;
}
Dog.prototype = {work:function(){alert("I am working!")}}或者
Dog.prototype.work = function(){
alert("I am working");
}
2.js中构造函数在初始化的时候加new和不加new的区别
function Dog(name,age){
this.name = name;
this.age = age;
}
Dog.prototype = {work:function(){alert("I am working!")}}
var dog1 = Dog("dog1",12);//这只是相当于调用普通函数，原型work不会生成，调用work属性会报错
var dog1 = new Dog("dog2",13);//这里是调用构造函数，初始化原型work