JavaScript learning summary prototype_javascript skills

Prototype in JS is a difficult part to understand in JS

This article is based on the following knowledge points:

1 Prototype design pattern
In .Net, clone() can be used to implement the prototype method

The main idea of ​​the prototype method is that there is now a class A, and I want to create a class B, which is prototyped by A. And can be expanded. We call the prototype of B A.

2 JavaScript methods can be divided into three categories:
a -> class method

b -> Object method

c -> Prototype method

Example:

function People(name){ 

  //对象属性
  this.name=name; 

  //对象方法 
  this.Introduce=function(){

     alert("My name is "+this.name); 

  }

}
//类静态方法

People.Run=function(){ 

　　alert("I can run");

}

//原型方法

People.prototype.IntroduceChinese=function(){ 

 alert("我的名字是"+this.name);

} 

//测试

var p1=new People("Windking");

p1.Introduce();//调用对象方法

People.Run();//调用静态方法

p1.IntroduceChinese(); //调用原型方法

3. obj1.func.call(obj) method
means to treat obj as obj1 , when calling the func method, the func method of obj1 was originally called. However, after passing in obj, the context object was changed, and the method of ojb1 was called through the obj object.

Okay, let’s solve the problems one by one. :

What does prototype mean?

Every object in JavaScript has a prototype attribute. The explanation of the prototype attribute of an object in Javascript is: return a reference to the prototype of the object type.

A.prototype = new B();

Understanding prototype should not be confused with inheritance. The prototype of A is an instance of B. It can be understood that A has cloned all the methods and properties in B. A can use B's methods and properties. The emphasis here is on cloning rather than inheritance. This situation can occur: A's prototype is an instance of B, and B's prototype is also an instance of A.

Let’s look at an experimental example first:

function baseClass(){

  this.showMsg = function(){

    alert("baseClass::showMsg");  

  }

}

function extendClass(){

}

extendClass.prototype = new baseClass();

var instance = new extendClass();

instance.showMsg(); // 显示baseClass:showMsg

We first define the baseClass class, and then we define extentClass, But we plan to use an instance of baseClass as the prototype, and the extendClass we clone also contains the showMsg object method.

extendClass.prototype = new baseClass() can be read as: extendClass is created by cloning an instance of baseClass as the prototype.

Then there will be a question, what if extendClass itself contains a method with the same name as the method of baseClass?

The following is extended experiment 2:

function baseClass(){

  this.showMsg = function(){

    alert("baseClass::showMsg");  

  }

}

function extendClass(){

  this.showMsg =function (){

    alert("extendClass::showMsg");

  }

}

extendClass.prototype = new baseClass();

var instance = new extendClass();

instance.showMsg();//显示extendClass::showMsg

Experimental proof: When the function is run, it will first search for the function in the ontology. If it is found, it will be run. If it cannot be found, it will search for the function in the prototype. Or it can be understood that the prototype will not clone the function with the same name.

Then there will be a new question:

What if I want to use an instance instance of extendClass to call the object method showMsg of baseClass? ?

The answer is you can use call:

extendClass.prototype = new baseClass();

var instance = new extendClass();

var baseinstance = new baseClass();

baseinstance.showMsg.call(instance);//显示baseClass::showMsg

baseinstance.showMsg.call(instance) here; Read as "Call instance as baseinstance and call its object method showMsg"

Okay, someone may ask here, why not use baseClass.showMsg.call(instance);

This It’s the difference between object methods and class methods. What we want to call is the object method of baseClass

Finally, If you understand the following code clearly, then you can understand what this article says:

function baseClass(){

  this.showMsg = function(){

    alert("baseClass::showMsg");  

  }

  

  this.baseShowMsg = function() {

    alert("baseClass::baseShowMsg");

  }

}

baseClass.showMsg = function(){

  alert("baseClass::showMsg static");

}

function extendClass(){

  this.showMsg =function (){

    alert("extendClass::showMsg");

  }

}

extendClass.showMsg = function(){

  alert("extendClass::showMsg static")

}

extendClass.prototype = new baseClass();

var instance = new extendClass();

instance.showMsg(); //显示extendClass::showMsg

instance.baseShowMsg(); //显示baseClass::baseShowMsg

instance.showMsg(); //显示extendClass::showMsg

baseClass.showMsg.call(instance);//显示baseClass::showMsg static

var baseinstance = new baseClass();

baseinstance.showMsg.call(instance);//显示baseClass::showMsg

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