建構函式如果採用以下這種方式宣告，並不能為Point類生成一個名name為‘y1’的屬性property。

Object.assign(Point.prototype, {
  constructor(x,y){
         this.x=x;
         this.y1=y;
     },
  fun1(){}
});

完整demo如下：macOs+chrome（啟動devtools除錯，option+command+i）

// let methodName = 'getSum'

class Point{
     constructor(x,y){
         this
 
.x=x;
         this.y=y;
     }

    add(a, b){
        return a+b;
    }

    get(){
      return this.x+this.y;
    }
    get1(){
      return this.y1+this.y
    }
   

}
Object.assign(Point.prototype, {
  constructor(x,y){
         this.x=x;
         this.y1=y;
     },
  fun1(){}
});
Point.prototype.fun2 
 
= function(){}


var p = new Point(1,2);
console.log(Object.keys(Point.prototype))
console.log(Object.getOwnPropertyNames(Point.prototype))
console.log(Object.getOwnPropertyNames(p))
console.log(Object.getOwnPropertyNames(new Point(3,4)))
console.log(p.hasOwnProperty("x"))
console.log(p.hasOwnProperty(
 
"y"))
console.log(p.hasOwnProperty("y1"))
console.log(p.get())
console.log(p.get1())

結果：

(2)['fun1', 'fun2']
(6)['constructor', 'add', 'get', 'get1', 'fun1', 'fun2']
(2)['x', 'y']
(2)['x', 'y']
true
true
false
3
NaN
undefined