Brief analysis of classes and objects in JavaScript

1. Constructor method
This is a classic method and a method that must be taught 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 read the series of articles I wrote "Javascript Object-Oriented Programming", so I won’t go into details here. Its main disadvantage is that it is relatively complicated, 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, the fifth edition of the international standard ECMAScript for Javascript (the third edition is currently popular), was proposed 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, directly use Object.create() to generate an instance 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, and cannot share data between instance objects. The simulation of "classes" is not comprehensive enough. .
3. Minimalist approach
Dutch programmer Gabor de Mooij proposed a new method that is better than Object.create(). He called this method the "minimalist approach". This is also the method I recommend.
3.1 Encapsulation
This method does not use 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 createNew() to generate instances.

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

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

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

When used, 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.
3.2 Inheritance
Let one class inherit another class, which is very convenient to implement. Just call the latter's createNew() method in the former's createNew() method.
First define an Animal class.

　var Animal = {
　　　　createNew: function(){
　　　　　　var animal = {};
　　　　　　animal.sleep = function(){ alert("睡懒觉"); };
　　　　　　return animal;
　　　　}
　　};

Then, in Cat’s createNew() method, call Animal’s createNew() method.

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

The Cat instance obtained in this way will inherit both the Cat class and the Animal class.

var cat1 = Cat.createNew();
　　cat1.sleep(); // 睡懒觉

3.3 Private properties and private methods
In the createNew() method, as long as the methods and properties are not defined on the cat object, they are private.

　　var Cat = {
　　　　createNew: function(){
　　　　　　var cat = {};
　　　　　　var sound = "喵喵喵";
　　　　　　cat.makeSound = function(){ alert(sound); };
　　　　　　return cat;
　　　　}
　　};

The internal variable sound in the above example cannot be read externally and can only be read through the public method makeSound() of cat.

　var cat1 = Cat.createNew();
　　alert(cat1.sound); // undefined

3.4 Data Sharing
Sometimes, we need all instance objects to be able to read and write the same internal data. At this time, just encapsulate the internal data inside the class object and outside the createNew() method.

　　var Cat = {
　　　　sound : "喵喵喵",
　　　　createNew: function(){
　　　　　　var cat = {};
　　　　　　cat.makeSound = function(){ alert(Cat.sound); };
　　　　　　cat.changeSound = function(x){ Cat.sound = x; };
　　　　　　return cat;
　　　　}
　　};

Then, two instance objects are generated:

　　var cat1 = Cat.createNew();
　　var cat2 = Cat.createNew();
　　cat1.makeSound(); // 喵喵喵

At this time, if there is an instance object, modify Without shared data, another instance object will also be affected.

　　cat2.changeSound("啦啦啦");
　　cat1.makeSound(); // 啦啦啦

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