function Person1(name,age){
        this.name = name;
        this.age = age;
        if (typeof this.sayName != ‘function‘)
        {
            Person1.prototype.sayName = function(){
                console.log(this.name);
            }
        }
    }

function Person1(name,age){
        this
 
.name = name;
        this.age = age;
        if (typeof this.sayName != ‘function‘)
        {
            Person1.prototype = {
                sayName:function(){
                    console.log(this.name);
                }
            }
        }
    }

上邊和下邊不一樣，下邊會斷開以前的原型的指針，因為{}就是一個對象

動態原型模式