js继承的几种方法

1.原型链继承：子类对象指向父类的实例以实现继承

function Parent()
{
    this.sayAge = function()
    {
        console.log(this.age)
    }
};
function Child(firstname)
{
    this.firstname = firstname;
    this.age = 10;
    this.say = function()
    {
        this.sayAge();//继承父类sayAge
        console.log(this.firstname)
    }
}
Child.prototype = new Parent();//子类对象指向父类实例
var people = new Child("张三");   //实例化子类时参数不能传递给父类
people.say();

2.call继承   类似于apply继承

function Parent(firstname)
{
    this.firstname = firstname;
    this.age = 40;
    this.sayAge = function()
    {
        console.log(this.age);
    }
}
function Child()
{

    this.say = function()
    {
        console.log(this.firstname);
        this.sayAge();
    }

}
var child = new Child();
Parent.call(child,'张三');
child.say();

3.混合模式实现继承（原型链和call）

function Parent()
{

    this.sayAge=function()
    {
        console.log(this.age);
    }
}

Parent.prototype.sayParent=function()
{
   console.log("this is parentmethod!!!");
}

function Child(firstname)
{
    Parent.call(this);
    this.firstname=firstname;
    this.age=40;
    this.saySomeThing=function()
    {
        console.log(this.firstname);
        this.sayAge();
    }
}

Child.prototype=new  Parent();
var child=new Child("张");
child.saySomeThing();
child.sayParent();

 

call解析

    var func=new function()
    {
        this.a="func"
    }; 
    var myfunc=function(x)
    {  
        var a="myfunc";  
        alert(this.a);  
        alert(x);  
    }  
    myfunc.call(func,"var");//myfunc 父类   func子类（当前对象）func继承父类的方法  ‘var’传递给父类的参数