A first look at prototypes and prototype chains: learn their functions from the basics

Introduction to prototypes and prototype chains: understand their role from scratch, need specific code examples

Introduction:
When learning JavaScript, you often hear The concepts of prototype and prototype chain are one of the core points of understanding JavaScript. However, for beginners, these concepts can be somewhat abstract and complex. This article will start from scratch and introduce the role of prototypes and prototype chains and how to use them through specific code examples to help readers better understand the prototype mechanism in JavaScript.

1. Prototype
In JavaScript, objects are created through constructors (Constructor). Every constructor has a property called prototype, which points to an object. This object can contain arbitrary properties and methods.

1. The relationship between constructor and prototype
   There is an important connection between the constructor and the prototype. All objects created by the constructor can access the properties and methods in this prototype object. We can create multiple objects through the constructor. These objects share the same prototype object and can use the properties and methods defined in the prototype object.

The following is an example where two objects are created through the constructor and they share the same prototype object:

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

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

var person1 = new Person("Alice", 20);
person1.sayHello();  // 输出：Hello, my name is Alice, I am 20 years old.

var person2 = new Person("Bob", 25);
person2.sayHello();  // 输出：Hello, my name is Bob, I am 25 years old.

2. The role of prototype
3. Implementation Sharing of attributes and methods: Through the prototype, the attributes and methods required by the object can be defined on the prototype object, thereby realizing the sharing of attributes and methods between objects and saving memory space.
4. Expand the function of the object: By adding additional properties and methods to the prototype object, the function of the object can be extended without changing the original object structure.

2. Prototype Chain
The prototype chain is a mechanism that connects objects through prototype attributes. When accessing a property of an object, if the object itself does not have this property, JavaScript will look up the prototype chain until it finds the property or reaches the top of the prototype chain.

1. Creation and access of the prototype chain
   Each object has an internal property called [[Prototype]], which points to the prototype object that the object inherits. Through this attribute, JavaScript creates the prototype chain.

We can access the prototype object through the __proto__ attribute of the object, or obtain the prototype object through the Object.getPrototypeOf(obj) method.

The following is an example that demonstrates the connection between objects through the prototype chain:

function Animal() {
  this.type = "animal";
}

Animal.prototype.sayType = function() {
  console.log("I am a " + this.type);
};

function Dog() {
  this.breed = "dog";
}

Dog.prototype = new Animal();

var dog = new Dog();
dog.sayType();  // 输出：I am a animal

2. The role of the prototype chain
3. Realize the inheritance of properties and methods: through Prototype chain, objects can inherit the properties and methods in their prototype objects, realizing code reuse and saving development time and code volume.
4. Realize multi-layer inheritance: Through the connection of the prototype chain, the inheritance relationship between multi-layer objects can be realized.

Conclusion:
Prototype and prototype chain are one of the core concepts of JavaScript and play an important role in understanding the objects and inheritance mechanism in JavaScript. By studying prototypes and prototype chains, we can better understand the creation and inheritance of objects in JavaScript, and be able to use prototypes and prototype chains to optimize and expand code.

I hope that through the explanation and specific code examples of this article, readers can better understand the role and usage of prototypes and prototype chains, and improve their abilities in JavaScript programming.

The above is the detailed content of A first look at prototypes and prototype chains: learn their functions from the basics. For more information, please follow other related articles on the PHP Chinese website!