Js-constructor problem

 function Fu(uname ,age ){ 
    //1. Instance member
    this.name =name ;
    this.age =age;
    this.sing=function(){
        console.log("Eat watermelon")}}//2. Instantiate different objects
// Create an object when new and return the instance
 let lj = new Fu('cole'.18);   
let ll =new Fu('李路'.19);
 // Call different instance objects with the same common method
 lj.sing()
 ll.sing()
 // Constructor faults
// (1) There is a memory waste problem
 // (2

Copy the code

‘// Solve the constructor waste memory problem

• 1: javaScript dictates that every constructor has a prototype property that points to the prototype object, so you just define the method to that prototype
• Prototype. Method name =function(){}
• For each instantiation object (e.g. Lj) the system adds its own __proto__ to our constructor prototype object (e.g. Fu.prototype).
• console.log(lj.proto === Fu.prototype); To true
• Note: Instantiate object (__proto__) constructor prototype object (prototype object)
• As shown in figure

• Note: the __proto__ lookup mechanism first looks for sing in the instance object, and then looks for sing in the constructor prototype object

• Note: __proto__ cannot be assigned only to the reference constructor prototype object

• The prototype object has a constructor property that points to the constructor itself

• Note: The constructor property (_proto) and the constructor property (prototype) refer to the constructor itself. Prototype ={constructor :Fu}. Prototype ={constructor :Fu}

• Prototype chain diagram: below