How to implement inheritance in javascript? A brief analysis of various methods

Before talking about JavaScript inheritance, we need to first understand what a class is. In common programming languages, such as Java, C, C#, etc., a class is a program structure used to encapsulate data and methods. Objects can be created through instantiation to achieve code reuse and abstraction.

But in JavaScript, classes are defined and used slightly differently than in other languages. JavaScript classes are based on objects, and objects are at the center of the language. JavaScript does not have such a complicated class inheritance system, and all classes can be inherited. That is to say, except for some specific built-in objects, such as Math, Date, etc., most objects in JavaScript can serve as base classes.

In JavaScript, inheritance has the following methods:

1. Prototype chain inheritance:

Prototype chain inheritance is the most basic inheritance method in JavaScript. Use prototypes to implement function and property inheritance from parent classes. Simply put, the prototype of the subclass points to the instance of the parent class, thereby achieving inheritance. In this way, you can extend the parent class and add new attributes and methods.

For example:

function Animal() {
  this.species = "动物";
}

function Cat(name, color) {
  this.name = name;
  this.color = color;
}

Cat.prototype = new Animal();  // 将 Cat 的原型对象指向 Animal 的实例

var cat1 = new Cat('小红', '黑色');
console.log(cat1.species);  // 输出 "动物"

2. Borrowed constructor inheritance:

Borrowed constructor inheritance, also called classic inheritance or stolen constructor inheritance, refers to the Inheritance is achieved by calling the constructor of the parent class in the constructor of the subclass. This method is different from prototype chain inheritance. It can inherit the attributes of the parent class and achieve attribute independence.

For example:

function Animal(name, color) {
  this.name = name;
  this.color = color;
}

function Cat(name, color) {
  Animal.call(this, name, color);  // 在 Cat 类的构造函数中调用 Animal 类的构造函数
}

var cat1 = new Cat('小红', '黑色');
console.log(cat1.name);   // 输出 "小红"
console.log(cat1.color);  // 输出 "黑色"

3. Combined inheritance:

Combined inheritance refers to combining prototype chain inheritance and borrowed constructor inheritance, so that At the same time, it inherits the properties and methods of the parent class, and can use the properties and methods of the parent class.

For example:

function Animal(name, color) {
  this.name = name;
  this.color = color;
}

Animal.prototype.eat = function() {
  console.log('我是一只动物，我可以吃东西！');
}

function Cat(name, color) {
  Animal.call(this, name, color);
}

Cat.prototype = new Animal();
Cat.prototype.constructor = Cat;

var cat1 = new Cat('小红', '黑色');
console.log(cat1.name);   // 输出 "小红"
console.log(cat1.color);  // 输出 "黑色"
cat1.eat();              // 输出 "我是一只动物，我可以吃东西！"

4. Parasitic inheritance:

Parasitic inheritance refers to creating a function that is only used to encapsulate the inheritance process. In this function Enhance the object in some way and finally return this object. This object can be used as a prototype object for subclasses to achieve inheritance.

For example:

function Animal(name) {
  var obj = {
    name: name,
    eat: function() {
      console.log('我是一只动物，我可以吃东西！');
    }
  };
  return obj;
}

function Cat(name, color) {
  var animal = Animal.call(this, name);
  animal.color = color;
  return animal;
}

var cat1 = new Cat('小红', '黑色');
console.log(cat1.name);   // 输出 "小红"
console.log(cat1.color);  // 输出 "黑色"
cat1.eat();              // 输出 "我是一只动物，我可以吃东西！"

5. Parasitic combination inheritance:

Parasitic combination inheritance refers to parasitic inheritance based on combination inheritance. Optimize object inheritance performance. Inheritance can be achieved by creating a new object that inherits the prototype of the parent class, avoiding the pitfalls of initializing the object when calling the parent class constructor.

For example:

function Animal(name) {
  this.name = name;
}

Animal.prototype.eat = function() {
  console.log('我是一只动物，我可以吃东西！');
};

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

Cat.prototype = Object.create(Animal.prototype);
Cat.prototype.constructor = Cat;

var cat1 = new Cat('小红', '黑色');
console.log(cat1.name);   // 输出 "小红"
console.log(cat1.color);  // 输出 "黑色"
cat1.eat();              // 输出 "我是一只动物，我可以吃东西！"

In summary, JavaScript inheritance can be implemented in a variety of ways. In actual development, you need to choose the appropriate method according to specific scenarios and needs.

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