What are prototypes and prototype chains? How to inherit properties and methods of an object?

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⭐ Introduction to the column

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⭐ Prototype and Prototype Chain

In JavaScript, prototypes and prototype chains are important concepts for understanding object inheritance.

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⭐ Prototype

Every JavaScript object has an associated prototype object, which is a reference to other objects. A prototype object is a special object that stores shared properties and methods for sharing and inheritance by other object instances. Through prototypes, you can realize the reuse of properties and methods between objects.

In JavaScript, the prototype of an object can prototypebe accessed through the property, and function objects (including constructors) have a prototypeproperty, which is the prototype object used when creating an object instance.

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

Person.prototype.sayHello = function() {
    
    
  console.log(`Hello, my name is ${
      
      this.name}`);
};

const person1 = new Person('Alice');
const person2 = new Person('Bob');

person1.sayHello(); // 输出：Hello, my name is Alice
person2.sayHello(); // 输出：Hello, my name is Bob

In the above example, Person.prototypeit is the prototype of person1and person2, which contains sayHellothe method, so these two objects can inherit and share this method.

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⭐ Prototype Chain

The prototype chain is a mechanism for the inheritance relationship between objects. When you access a property or method of an object, JavaScript first looks in the object itself, and if it can't find it, it looks up the prototype chain until it finds the property or method or reaches the top of the prototype chain (usually) Object.prototype.

For example, if you try to access person1a property or method of , JavaScript first looks to see if the object itself has the property or method, and if not, it walks the prototype chain to find the method Person.prototypeon sayHello.

person1.sayHello(); // 输出：Hello, my name is Alice
person2.sayHello(); // 输出：Hello, my name is Bob

A prototype chain is a chain of prototype objects, each of which has a reference to its prototype. When you access a property or method, JavaScript searches in the order of the prototype chain.

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⭐ Inheritance properties and methods

To inherit the properties and methods of an object, you can do the following:

1. Constructor inheritance : By defining a constructor and using newthe keyword to create an object instance, the properties and methods of the constructor are inherited.

   function Animal(name) {
         
         
     this.name = name;
   }
   
   Animal.prototype.sayName = function() {
         
         
     console.log(`My name is ${
           
           this.name}`);
   };
   
   function Dog(name, breed) {
         
         
     Animal.call(this, name); // 调用父类构造函数，继承属性
     this.breed = breed;
   }
   
   // 继承方法
   Dog.prototype = Object.create(Animal.prototype);
   Dog.prototype.constructor = Dog; // 修复constructor属性
   
   const dog1 = new Dog('Buddy', 'Golden Retriever');
   dog1.sayName(); // 输出：My name is Buddy
   

2. Class inheritance (the way after ES6): use the class ( class) syntax to define the constructor and method of the object.

   class Animal {
         
         
     constructor(name) {
         
         
       this.name = name;
     }
   
     sayName() {
         
         
       console.log(`My name is ${
           
           this.name}`);
     }
   }
   
   class Dog extends Animal {
         
         
     constructor(name, breed) {
         
         
       super(name); // 调用父类构造函数，继承属性
       this.breed = breed;
     }
   }
   
   const dog1 = new Dog('Buddy', 'Golden Retriever');
   dog1.sayName(); // 输出：My name is Buddy
   

These methods allow you to create objects with inheritance relationships, where child objects can access the properties and methods of the parent object. When using class inheritance, superthe keyword is used to call the parent class constructor.

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⭐ Written at the end

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