What are the three methods of defining a class in javascript

Three ways to define a class in JavaScript: 1. Use the constructor to define the class, the syntax is "function name(){this.name=value;}"; 2. Use the "Object.create()" method Define the class; 3. Use the "createNew()" method to define the class.

The operating environment of this tutorial: Windows 10 system, JavaScript version 1.8.5, Dell G3 computer.

What are the three methods of defining a class in javascript

In object-oriented programming, a class is a template of an object and defines the same group of objects (also called "instances") ) common properties and methods.

The JavaScript language does not support "classes", but you can use some workarounds to simulate "classes".

1. Constructor method

This is a classic method and a must-teach method in textbooks. It uses a constructor to simulate a "class" and uses the this keyword internally to refer to the instance object.

function Cat(){
  this.name = "大毛";
}

When generating an instance, use the new keyword.

var cat1 = new Cat();
alert(cat1.name);   //大毛

The attributes and methods of the class can also be defined on the prototype object of the constructor.

Cat.prototype.makeSound = function(){
  alert("喵喵喵");
}

For a detailed introduction to this method, please see the series of articles "JavaScript Object-Oriented Programming", I won’t go into details here. Its main disadvantage is that it is complicated to teach, uses this and prototype, and is very laborious to write and read.

2. Object.create() method

In order to solve the shortcomings of the "constructor method" and generate objects more conveniently, JavaScript The fifth edition of the international standard ECMAScript (the third edition is currently popular) proposes a new method Object.create().

Using this method, "class" is an object, not a function.

var Cat = {
  name: "大毛",
  makeSound: function(){
    alert("喵喵喵");
  }
};

Then, use Object.create() to generate an instance directly, without using new.

var cat1 = Object.create(Cat);
alert(cat1.name);   //大毛
cat1.makeSound();   //喵喵喵

Currently, the latest versions of all major browsers (including IE9) have deployed this method. If you encounter an old browser, you can use the following code to deploy it yourself.

if(!Object.create){
  Object.create = function(o){
    function F(){};
    F.prototype = o;
    return new F();
  }
}

This method is simpler than the "constructor method", but it cannot implement private properties and private methods, nor can it share data between instance objects, and the simulation of "classes" is not comprehensive enough.

3. Minimalist Method

Dutch programmer Gabor de Mooij proposed a new method that is better than Object.create() method, which it calls the "minimalist approach". This is also the method I recommend.

3.1 Encapsulation

This method does not apply to this and prototype, and the code is very simple to deploy. This is probably why it is called the "minimalist method".

First of all, it also uses an object to simulate a "class". In this class, define a constructor caeateNew() to generate instances.

var Cat = {
  createNew: function(){
    //some code here
  }
};

Then, in carateNew(), define an instance object and use this instance object as the return value.

var Cat = {
  createNew: function(){
    var cat = {};
    cat.name = "大毛";
    car.makeSound = function(){
      alert("喵喵喵")；
    }；
  }
}；

When using it, call the createNew() method to get the instance object.

var cat1 = Cat.createNew();
cat1.makeSound();   //喵喵喵

The advantage of this method is that it is easy to understand, has a clear and elegant structure, and conforms to the traditional "object-oriented programming" construct, so the following features can be easily deployed.

Related recommendations: javascript learning tutorial

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