Analysis of the differences and functions of prototypes and prototype chains

Analysis of the difference and role of prototype and prototype chain

In JavaScript, prototype and prototype chain are very important concepts in object-oriented programming. They are not only the basis for understanding objects and inheritance in JavaScript, but also the key to a deeper understanding of JavaScript. This article will use specific code examples to analyze the differences and functions of prototypes and prototype chains.

1. Prototype

Prototype is the basis of inheritance between objects in JavaScript. Every object has a prototype, which can be accessed through the __proto__ attribute. A prototype is an ordinary object that contains the properties and methods of the inherited object.

The following is a simple sample code:

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

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

var person = new Person("Alice", 18);
person.sayHello(); // 输出: Hello, my name is Alice

In this example, Person.prototype is a prototype object that contains the sayHello method . The person object constructs an instance through the new keyword and inherits the methods in Person.prototype through the prototype chain.

2. Prototype chain

The prototype chain is a mechanism that associates objects through prototypes. The prototype of an object can also be another object, and this association is connected through the __proto__ attribute. When we access a property or method of an object, if the current object does not have one, we will look up along the prototype chain until we find the definition of the property or method.

Continue to use the above sample code below:

function Student(name, age, grade) {
  Person.call(this, name, age);  // 调用父类的构造函数
  this.grade = grade;
}

Student.prototype = Object.create(Person.prototype);  // 继承父类的原型

Student.prototype.sayGoodbye = function() {
  console.log("Goodbye, my name is " + this.name);
};

var student = new Student("Bob", 20, 5);
student.sayHello();  // 输出: Hello, my name is Bob
student.sayGoodbye();  // 输出: Goodbye, my name is Bob

In this example, we define a Student class, which passes Person.call(this, name, age)Call the constructor of the parent class and inherit the prototype of the parent class through Object.create(Person.prototype). In this way, the Student instance objectstudent can access and use the methods defined in the parent class Person.

3. Difference and function

The relationship between prototype and prototype chain is that each object has a prototype, and the prototype can be used to define shared properties and methods. The prototype chain is a linked list structure composed of the prototypes of multiple objects.

The role of prototype is to share attributes and methods between objects, which can reduce memory consumption and improve code reusability. Objects inherit the properties and methods of parent objects through the prototype chain, which can achieve effects similar to class inheritance and method rewriting in traditional object-oriented programming.

The role of the prototype chain is to realize the inheritance relationship between properties and methods between objects. When we access the properties or methods of an object, the JavaScript engine will search in the order of the prototype chain to ensure that we can access The correct property or method.

Summary:

• Prototype is a property that every object has. It defines the methods and properties shared by objects.
• The prototype chain is connected through the prototype properties of objects, forming a mechanism of object inheritance.
• The relationship between prototype and prototype chain enables JavaScript to achieve powerful object-oriented programming capabilities.

Through the explanation and sample code of this article, we can better understand and apply the role of prototype and prototype chain in JavaScript, which is very important for mastering objects and inheritance in JavaScript.

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