JavaScript strictly speaking does not have classes

With the popularity and widespread use of JavaScript, more and more developers are beginning to pay attention to some features and limitations of the JavaScript programming language. One of them is whether there is a concept of a class, which is a hotly debated question. In this article, we will delve deeper into this topic to understand the true nature of JavaScript classes.

JavaScript is a very flexible programming language with powerful features, such as closures, higher-order functions, and prototypal inheritance, which are the core features of JavaScript. Unlike other programming languages, JavaScript has extremely high complexity in different paradigms. Is it a strictly object-oriented language?

For many developers, classes are the key to many object-oriented programming languages. basic concepts. Languages ​​such as Python, C#, and Java have classes that allow you to define properties, methods, and create new instances. Classes provide some of the benefits of code reusability and extensibility because they allow programmers to separate code into modules, abstractions, and reuse. But when we talk about JavaScript, strictly speaking there is no such thing as a class.

What is a class?

In order to better understand this problem, we need to first understand what a class is. A class is a representation of an object model and a special data structure that can describe the characteristics (properties) and behavior (methods) of an object.

In the class hierarchy, the upper parent class will define some common properties and methods, and these common properties and methods can be inherited and used by subclasses. Subclasses can redefine or inherit these properties and methods, and can add their own properties and methods.

For example, the following is an example of a class written in Java:

public class Person{
  private String name;
  private int age;
  
  public Person(String name, int age) {
    this.name = name;
    this.age = age;
  }
  
  public String getName() {
    return this.name;
  }
  
  public int getAge() {
    return this.age;
  }
  
  public void sayHello() {
    System.out.println("Hello, my name is " + this.name);
  }
}

In this example, we define a Person class, which contains two attributes: name and age, and two Methods getName() and getAge(). It also has a sayHello() method, which prints the name of the Person instance to the console.

Objects in JavaScript

Some people may think that JavaScript is a comprehensive object-oriented language, which is a misunderstanding. Although JavaScript uses a syntactic structure similar to classes, its real object model is based on prototypes.

In JavaScript, objects are created at runtime based on a JavaScript function. It does not have an explicit class definition, but uses constructors to create new objects. Inside the constructor, you can define the initial properties and methods of an object as the basic definition of the object.

For example, the following example is a Person object defined by a JavaScript constructor:

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

Person.prototype.getName = function() {
  return this.name;
};

Person.prototype.getAge = function() {
  return this.age;
};

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

As you can see, a Person object based on the constructor is created in JavaScript. In this function, we set the name and age properties and assign them to the newly created object using the "this" keyword. Then, we use the Person.prototype object to define three methods for the newly created Person.

Prototypal inheritance

In JavaScript, inheritance is a non-traditional way, implemented using prototypal inheritance. Prototypal inheritance is implemented because all JavaScript objects have a prototype object.

Every JavaScript object has a prototype object, which contains the properties and methods of the object. When we create a new object, its original prototype is empty and it inherits members from the prototype of the constructor. Any other objects can continue to define their own properties and methods.

For example, the following code demonstrates how to add new properties and methods to a created object through prototypal inheritance:

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

Person.prototype.getName = function() {
  return this.name;
};

Person.prototype.getAge = function() {
  return this.age;
};

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

Person.prototype.setAge = function(newAge) {
  this.age = newAge;
};

In this example, we add a method named setAge() method and add it to the Person prototype object. Now we can use this method to set a new age for the Person object.

Conclusion

Strictly speaking, JavaScript does not have a class. This is due to the special design of JavaScript. In JavaScript, objects are created based on prototype variables, and prototypal inheritance is used to implement the inheritance relationship between objects. As a result, JavaScript provides a very flexible programming model, allowing programmers to implement different programming paradigms in different functions.

The core concept of JavaScript object-oriented programming is not classes, but objects. Therefore, when implementing complex JavaScript applications, you need to master the skills of how to create and inherit objects by becoming familiar with JavaScript's prototypal inheritance mechanism. This is the key to writing efficient JavaScript code.

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