An in-depth analysis of the prototype chain mechanism in JavaScript

Detailed explanation of prototype prototype chain in JS

In Javascript, each object has a prototype (prototype). The prototype is an object that contains shared properties and Method, prototype chain is a mechanism that allows objects to inherit and share properties and methods.

The prototype chain is implemented through the _proto_ attribute of each object, which points to the prototype of the object. If an object cannot find the required property or method, it continues along the prototype chain until it finds or reaches the end of the prototype chain.

Let’s look at an example to create a constructor called Person and its instance object:

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

var person1 = new Person('Alice', 25);

When using the new operator to create a person1 object, the following operations will be performed:

1. Create an empty object person1.
2. Point the _proto_ attribute of person1 to the prototype of the Person constructor, which is Person.prototype.
3. Execute the Person constructor, point this to person1, and assign the name and age attributes.

In fact, Person.prototype is the prototype of person1. We can add methods and attributes to the prototype:

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

Now, the person1 object can use the sayHello method:

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

When we call the person1.sayHello() method, Javascript first searches for this method in the person1 object. If it is not found, it will continue to search along the prototype chain in Person.prototype, and execute it after finding it.

If we add a new attribute in Person.prototype, person1 can also use it:

Person.prototype.gender = 'Female';
console.log(person1.gender);  // 输出: Female

The prototype chain can also implement inheritance, we can create a new constructor Student, and Let it inherit from Person:

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

Student.prototype = Object.create(Person.prototype);
Student.prototype.constructor = Student;

In the above code, we use the Object.create() method to create the Student.prototype object, point its _proto_ attribute to Person.prototype, and set the Student.prototype .constructor points to the Student constructor.

Now, we can create a student1 object and use the properties and methods inherited from Person:

var student1 = new Student('Bob', 20, 'ABC School');

console.log(student1.name);   // 输出: Bob
console.log(student1.age);    // 输出: 20
student1.sayHello();          // 输出: Hello, my name is Bob
console.log(student1.school);  // 输出: ABC School

In the above example, the student1 object can access the properties and methods inherited from Person , the reason is that through the prototype chain, it can find these properties and methods.

The prototype chain is an important mechanism in Javascript to implement object inheritance and shared properties and methods. It makes the code more efficient and flexible. When writing Javascript code, it is very important to have a deep understanding of the prototype chain.

Summary:

• Every object has a prototype. The prototype is an object that contains shared properties and methods.
• Through the _proto_ attribute of the object, the prototype chain can be realized to realize the inheritance and sharing of attributes and methods.
• The prototype chain is a mechanism to implement object inheritance and shared properties and methods in Javascript.

I hope that through the explanation of this article, you will have a deeper understanding of the prototype chain in Javascript.

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