javascript - 构造函数中的构造函数 - 不好的做法？

Question

我正在探索一些代码，我看到了将一个构造函数嵌入另一个构造函数的做法多次使用:

/**
 * @constructor
 */
function contact_duplicates_manager(global_objects)
{
    this.field_processors =
    {
        "Phone1Number": new phone_processor(),
        "Phone2Number": new phone_processor(),
        "Phone3Number": new phone_processor()
    }
    //...here some other code

    /**
     * @constructor
     */
    function phone_processor()
    {
        //...here some other code

        function clear_phone(phone)
        {
            //...here some code
        }
        this.is_equals = function (value1, value2) 
        {
            return is_equals(clear_phone(value1), clear_phone(value2));
        }
    }
}

//... later in the code
var valid = this.field_processors[fld_name]["is_equals"](native_value, custom_value)

你认为 phone_processor 构造函数应该在 contact_duplicates_manager 之外吗？

Answer 1

Do you think phone_processor function constructor should be outside contact_duplicates_manager?

是的。虽然有效且有效，但效率不高且可能不可读。通过嵌套，每个 contact_duplicates_manager 实例都有 phone_processor，它们具有不同的构造函数并继承自不同的原型(prototype)对象。这对于构造函数工厂或类似模式可能是必需的，但这些非常罕见，我怀疑您在这里需要它。

我的经验法则:

• Move every function that does not need access to any local closure variable to a higher scope.
• If you don't want it to be public in there, use an intermediate scope of an IEFE.
• If you need a constructor inside the scope of a multiple-times-executed function, try to share the prototype object among the constructors, and do not leak a local constructor.

最后一条规则的例子:

function Item(…) {…}
function Store {
    var that = this;
    this.items = [];
    this.addItem = function(…) {
        that.items.push(new LocalItem(…));
    };
    function LocalItem(…) {
        Item.call(this, …);
        this.store = that;
    }
    LocalItem.prototype = Item.prototype;
}

您不一定需要您称为类继承的全局 Item 函数，有时需要一个全局 proto 对象，您可以将其分配给 LocalConstructor。原型(prototype)就够了。