Does javascript have a way to define a class?

Javascript has methods for defining classes. Method: 1. Use the constructor to define the class, the syntax is "function name() {this.name = "...";}"; 2. Use the "Object.create()" method to define the class, the syntax is "var name = Object.create(...);"; 3. Define a constructor in the class, define an instance object in the function, and then call the function again to define the class.

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

Does javascript have a way to define a class?

Javascript has a way to define a class

There are three ways to define a class in Javascript

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

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 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");
　　}

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, Javascript The fifth edition of the international standard ECMAScript 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 he called 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 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.

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. It 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 one instance object modifies the shared data, the other instance object will also be affected.

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

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