Javascript原型和访问类的问题

Question

Family = function(name) {
  this._Name = name;
}

Family.prototype = {
  getName: function() {
    return this._Name;
  },
  People: function(num) {
    this._Number = num;
  }
}

Family.People.prototype = {
  clearNumber: function() {
    this._Number = 0;
  }
}

人是一个嵌套的类.它的父类是Family.

我得到了Family.People未定义的错误.有人可以纠正上面的代码吗？

Answer 1

工作代码

// function doesn't need "new" operator
var Family = function(name) { this._Name = name; };

Family.prototype = {
    getName: function() { return this._Name; }, // missing comma
    People: function(num) {
        this._Number = num;
    }
};

// work with prototypes
Family.prototype.People.prototype = {
    clearNumber: function() { this._Number = 0; }
};

这会奏效.但是你必须要注意,当你打电话时:

var f = new Family("Doe");

f.People它只是一个对象构造函数,而不是某个其他对象的实例.你必须实例化它,如:

f.members = new f.People(3);

你在你的实例中有一个构造函数,这是相当混乱的.

更好的方法

因此,如果您以这种方式编写原型可能会更好:

var Family = function(name) {
    this._Name = name;
    this.getName = function() { return this._Name; };
};

Family.People = function(num) {
    this._Number = num;
    this.clearNumber = function() { this._Number = 0; };
};

这实际上是一个类(而不是实例)中的类.所以上线将以这种方式调用:

var f = new Family("Doe");
f.members = new Family.People(3);

向下钻取f实例看起来像:

f
  _Name
  getName()
  members
    _Number
    clearNumber()

私有变量

var Family = function(name) {
    var _name = name;
    this.getName = function() { return _name; };
};

Family.People = function(num) {
    var _num = num;
    this.getNumber = function() { return _num; }
    this.clearNumber = function() { _num = 0; };
};

通过这种方式,我们将变量设为私有且只能在其中访问,因此无法在外部进行操作.您必须始终使用函数来操作它们.这使得它更加健壮,尤其是当存在与变量值相关的某些业务规则时.

var f = new Family("Doe");
f._name; // this is undefined because "_name" is private closure variable

向下钻取f实例现在看起来更像是一个类对象实例:

f
  getName()
  members
    getNumber()
    clearNumber()

Answer 2

请注意,您正在分配Family.prototype.People然后尝试访问Family.People.

Family它不是一个实例,Family因此它没有该类的属性 - 因此您试图在该第三个语句中访问Family它的实例.(这有点简化)FunctionFunction.prototype.People

即你想要做的是

Family.prototype.People.prototype = {
  clearNumber:function(){this._Number = 0;}
}

你在人们面前也错过了一个逗号,但我认为这是一个错字...