In traditional javascript, there are only objects, not classes. It is a prototype based object-oriented language. The characteristic of prototype object is to share its own properties with new objects. Compared with other traditional object-oriented languages, this writing method has a unique feeling! Very confusing!
If you want to generate an object instance, you need to define a constructor first, and then complete it through the new operator. Constructor example:

 1 //The function name and instantiation construct name are the same and capitalized (not mandatory, but it helps to distinguish between constructors and ordinary functions)
 2 function Person(name,age) {
 3     this.name = name;
 4     this.age=age;
 5 }
 6 Person.prototype.say = function(){
 7     return "My name is" + this.name+"this year"+this.age+"Years old";
 8 }
 9 var obj=new Person("laotie",88);//To create an object through a constructor, you must use new operator
10 console.log(obj.say());//My name is laotie I'm 88 years old

Execution process of constructor generation instance:

1. When the constructor is used and the new constructor () is used, the background will implicitly execute new Object() to create the object;
2. The scope of the constructor is given to the new object (that is, the object created by new Object()), and this in the function body represents the object created by new Object().
3. Execute the code of the constructor.
4. Return a new object (returned directly in the background);

ES6 introduces the concept of class, which can be defined through the class keyword. The emergence of this keyword makes it clearer in object writing, and it is more like an object-oriented language. If the previous code is changed to ES6, it will look like this:

 1 class Person{//Defines a name Person Class of
 2     constructor(name,age){//constructor Is a construction method used to receive parameters
 3         this.name = name;//this Represents an instance object
 4         this.age=age;
 5     }
 6     say(){//This is a class method. Be careful not to add it function
 7         return "My name is" + this.name+"this year"+this.age+"Years old";
 8     }
 9 }
10 var obj=new Person("laotie",88);
11 console.log(obj.say());//My name is laotie I'm 88 years old

Note:

　　1. When declaring a method in a class, never add the function keyword to the method
 　　2. Methods should not be separated by commas, otherwise an error will be reported

As can be seen from the following code, a class is essentially a function. The class itself points to the constructor. So we can think that the class in ES6 is actually another way to write the constructor!

1 console.log(typeof Person);//function
2 console.log(Person===Person.prototype.constructor);//true

All methods of the class are defined on the prototype attribute of the class

1 Person.prototype.say=function(){//Defines a method with the same name as in the class. Successfully achieved coverage!
2     return "I'm here to prove it. What's your name" + this.name+"this year"+this.age+"Years old";
3 }
4 var obj=new Person("laotie",88);
5 console.log(obj.say());//I'm here to prove it. What's your name laotie I'm 88 years old

Of course, you can also add methods to the class through the prototype attribute

1 Person.prototype.addFn=function(){
2     return "I passed prototype Newly added method,Name is addFn";
3 }
4 var obj=new Person("laotie",88);
5 console.log(obj.addFn());//I passed prototype Newly added method,Name is addFn

You can also use object Assign method to dynamically add methods to the object

 1 Object.assign(Person.prototype,{
 2     getName:function(){
 3         return this.name;
 4     },
 5     getAge:function(){
 6         return this.age;
 7     }
 8 })
 9 var obj=new Person("laotie",88);
10 console.log(obj.getName());//laotie
11 console.log(obj.getAge());//88

The constructor method is the default method of the constructor of the class. It is called automatically when an object instance is generated by the new command.

1 class Box{
2     constructor(){
3         console.log("Lala, it's sunny today");//This line of code is executed when the object is instantiated.
4     }
5 }
6 var obj=new Box();