ES5 examples detail the various inheritance methods of JavaScript

As a lightweight scripting language, JavaScript has been pushed to new heights after the emergence of ES6 and node.js. Although the new class syntax format for generating objects appeared in ES6, it is still ES5 syntactic sugar, but we still need to start with the native implementation of JavaScript to understand its inheritance implementation. ES6 provides a more concise fixed class declaration method.

Different developers have different understandings of JavaScript inheritance. I think it is mainly divided into four types

 - 原型链继承
 - 对象冒充继承(构造函数继承 不过我不喜欢这个名字)
 - 组合继承
 - 寄生组合继承

For inheritance, you can declare an Animal in advance and then discuss different inheritances Method.

    let Animal = (function () {
      function Animal (name) {
        this.name = name || 'Animal';
        this.sleep = function(){
          console.log(this.name + '正在睡觉！');
        }
      }
      Animal.prototype.eat = function(food) {
        console.log(this.name + '正在吃：' + food);
      }
      return Animal;
    })()

1. Prototype chain inheritance

       let Cat = (function () {
         function Cat(){ 
         }
         Cat.prototype = new Animal();
         Cat.prototype.name = 'cat';
         return Cat;
       })()

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   原型链是 javascript 的典型继承方式, 这种继承方式的最大特点就是共享,所有事例共享原型对象中的所有属性和方法, 共享是它的最大优点 也是它的最大缺点, 正对我们的不同需求, 比如大多数情况下我们常常需要某些属性是子类特有的  而一些读取属性方法需要共享,--另外此种继承无法向父类传参,无法实现多继承

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2. Object impersonation inheritance

       let Cat = (function () {
         function Cat(name){
           Animal.call(this,name);
         }
         return Cat;
       })()

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   对象冒充继承就是简单的利用call或者apply方法实现继承,这种继承最大的特点正好与原型链继承相反不能继承原型属性/方法--非共享(子类自有一份), 同样这是它的优点也是它的缺点, 另外它解决了原型链继承中无法向父类传参的缺点, 并且可以实现某种意义上的多继承--(注意这种多继承是打引号的)

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3. Combined inheritance

       let Cat = (function () {
         function Cat(name){
           Animal.call(this, name);
         }
         Cat.prototype = new Animal();
         Cat.prototype.constructor = Cat;
         return Cat;
       })()

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   组合继承是比较好的继承, 他是原型链继承和对象冒充继承的合体, 合理的利用了这两种组合的特点(是特点不是优点^_^),既是子类的实例，也是父类的实例, 但有一个缺点就是调用了两次父类构造函数，生成了两份实例（子类实例将子类原型上的那份屏蔽了）造成内存浪费. 这也是用的最多的一种

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4. Parasite combination inheritance

       let Cat = (function () {
         function Cat(name){
           Animal.call(this, name);
         }
         (function(sub, sup){
           var Super = function(){};
           Super.prototype = sup.prototype;
           sub.prototype = new Super();
           sub.prototype.constructor = sub
         })(Cat, Animal)
         return Cat;
       })()

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Parasite combination inheritance is a sublimation of combination inheritance. I personally think it is a perfect inheritance method. , Improved combination inheritance memory waste problem ^_^

Related recommendations:

Why do you need to use javascript to implement inheritance? Detailed explanation of several inheritance methods with examples

javascript prototype chain inheritance method usage and disadvantages with detailed examples

Three inheritance methods and their advantages and disadvantages in js

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