The concept of prototypes

Prototype-related concepts

2. About object-oriented concepts
   • Class: In JS is the constructor function
     • In the traditional object-oriented language, a template is defined using something called a class. Then use the template to create the object.
     • Similar functionality is also in the construction method. It is therefore called the class

       // 在 java 中, 最小的代码单位是 类class Program {// 成员}

   • Instances (instance) and objects (object)
     • An instance typically refers to an object created by a constructor. We become an example of XXX constructors
     • An instance is an object. The object is a general term.
     • Instances and objects are a synonym
   • Key-value pairs and properties and methods
     • The set of key-value pairs in JS is called an object
     • If the value is data (not a function), the key-value pair is called the property
     • If the value is a function (method), the key value pair is called the method
   • Parent class and Child class
     • The traditional object-oriented language uses classes to implement inheritance. Then there is the concept of a parent class, a subclass
     • The parent class is also called the base class, and the subclass is also called the derived class
     • In JS, it is often called the parent object, the child object. Base object, derived object.
4. Prototype-related concepts
   • A mysterious object is called a "prototype attribute" for a constructor function.
     • The mysterious object is the prototype property of the constructor.
     • Abbreviation prototype
   • The mystery object is also related to the object created by the constructor.
     • What's the relationship?
     • The object created by the mysterious object for the constructor is called the prototype object.
     • Abbreviation prototype
   • Object inherits from its prototype
     • constructor-created object inherits the prototype property from the constructor
     • The object that the constructor creates inherits from the prototype object of the object
     • The object that the constructor creates for the object that is represented by the constructor's prototype property is two different objects
       • Members in the prototype that can be used directly by the instance object
       • That is, the instance object directly "contains" the members of the prototype.
       • So the instance object inherits from the prototype
       • Such inheritance is "Prototype inheritance"
6. Some questions
   • What is the {} constructor?
   • Every literal object has a constructor.
     • {} Object
     • [] Array
     • /./REGEXP
     • Function ... Function

How to use Prototypes

Why use prototypes?

To improve the reusability of code

Attributes are not placed on the prototype: properties represent features that are easily changed

method is placed on the prototype: The method is treated the same way, can be reused

1. Using the dynamic properties of objects
   • constructor. prototype.xxx = VVVV;
2. Use Direct replacement

    Student.prototype = { sayHello: function () {}, study: function () {} };

The concept of prototypes