js实现继承

Posted 2020-10-13 shmily-代码君

js作为一种弱类型语言，继承也是其较大的功能之一

 

首先定义一个父类

// 定义一个教师类
function Teacher (name) {
  // 属性
  this.name = name || ‘Jack‘;
  // 实例方法
  this.study= function(){
    console.log(this.name + ‘正在学习！‘);
  }
}

一：继承的方式

1，原型链继承：将父类的实例作为子类的原型

function Student(){ 
}

Student.prototype = new Teacher();

Student.prototype.name = ‘john‘;

测试
var student = new Student();
console.log(student.name);

2,构造继承 (call,apply) 使用父类的构造函数来增强子类的实例，等同于复制父类的实例属性给子类

function Student(name) {
　　Teacher.call(this);
　　this.name = name || "Tom"
}

var student = new Student();
console.log(student.name);

3,实例继承：为父类实例增加新特性作为子类实例返回

function Student(name){
  var instance = new Teacher();
  instance.name = name || ‘Tom‘;
  return instance;
}

// 测试
var student = new Student();
console.log(student.name);

4，拷贝继承

function Student(name){
  var teacher= new Teacher();
  for(var p in teacher){
    Student.prototype[p] = Teacher[p];
  }
  Student.prototype.name = name || ‘Tom‘;
}

// 测试
var student= new Student();
console.log(student.name);

5，组合继承  （通过调用父类的构造，继承父类的属性并保留传参的优点，然后通过将父类实例作为子类原型，实现函数复用

function Student(name){
  Teacher.call(this);
  this.name = name || ‘Tom‘;
}
Student.prototype = new Teacher();

// 测试
var student = new Student();
console.log(student.name);

6,寄生组合继承    通过寄生方式，砍掉父类的实例属性，这样，在调用两次父类的构造的时候，就不会初始化两次实例方法/属性，避免的组合继承的缺点

function Student(name){
  Teacher.call(this);
  this.name = name || ‘Tom‘;
}
(function(){
  // 创建一个没有实例方法的类
  var Super = function(){};
  Super.prototype = Teacher.prototype;
  //将实例作为子类的原型
  Student.prototype = new Super();
})();

// 测试
var student = new Student();
console.log(student.name);