call() 方法的使用

//javascript 中call用处不少，用一句话概括就是动态改变this.比如说：
/*------------------------------1 继承式-----------------------------*/
function cat(){
}
//做一个原型扩展
cat.prototype={
    food:"fish",
    say: function(){
        console.log("I love "+this.food);
    }
}
var blackCat = new cat;
blackCat.say();
//当我需要一条黑狗也说它喜欢什么时：
blackDog = {food:"bone"};
//我们不想对它重新定义say方法，那么我们可以通过call用blackCat的say方法：
blackCat.say.call(blackDog);
/*----------------------------2 替换式------------------------------*/
function oldName() {
    this.oldname = function(){
        console.log(this.name)
    }
}
function Person(name) {
    this.name = null;
    this.Init = function (name) {
        this.name = name;
    }
    this.Init(name);
}
var oneName = new oldName();
var lutong = new Person('lutong')
oneName.oldname.call(lutong)
/*--------------------------3 继承式----------------------------------*/
function NameShowing(){  
    this.showName = function(){  
        console.log(this.name);  
    }  
}  
function Person(name){  
    this.name = null;  
    this.Init = function(name){    
        this.name = name;    
    }    
    this.Init(name);    
};  
var jeremy = new Person("Jeremy")   
NameShowing.call(jeremy);  
jeremy.showName();
/*-----------------4 带有构造函数的参数 -------------------- */
function Person(name, age){  
    this.name = null;  
    this.age = null;  
    this.showPersonInfo = function(){  
        console.log("Name: " + this.name + "");  
        console.log("Age: " + this.age + "");  
    };  
    this.Init = function(){  
        this.name = name;  
        this.age = age;  
    };  
    this.Init();  
}  
var jeremy = new Object();  
Person.call(jeremy, "Jeremy", 20);  
jeremy.showPersonInfo();