为什么要使用非特权方法?

var myClass = function() {
    // private variable
    var mySecret = Math.random();

    // public member
    this.name = "Fred";

    // privileged function (created each time)
    this.sayHello = function() {
        return 'Hello my name is ' + this.name;
        // function also has access to mySecret variable
    };
}

在原型上定义函数时,只创建一次函数,并共享该函数的单个实例。

var myClass = function() {
    // private variable
    var mySecret = Math.random();

    // public member
    this.name = "Fred";
}

// public function (created once)
myClass.prototype.sayHello = function() {
    return 'Hello my name is ' + this.name;
    // function has NO access to mySecret variable
};

因此,在原型上定义一个函数会产生更少的对象,从而提供更好的性能。另一方面,公共方法不能访问私有变量。更多的例子和推理可以在这里找到: http://www.crockford.com/javascript/private.html