怎样理解构造函数

function Person(name){
    var name = name;
    var sayHello = function(){
        console.log("Hello, I‘m "+name);
    }
    sayHello();
}

Person(); // "success."

// 调用Array的静态方法
Array.isArray([1,2,3]); // True

function Person(name){
    this.name = name;
    this.sayHello = function(){
        console.log("Hello, I‘m "+name);
    };
}

var Hanmeimei = new Person("Hanmeimei");
Hanmeimei.sayHello(); // "Hello, I‘m Hanmeimei";