带有原型的Javascript函数继承

在Douglas Crockford的JavaScript:The Good Parts中，他建议我们使用函数继承。下面是一个例子：

var mammal = function(spec, my) {
    var that = {};
    my = my || {};

    // Protected
    my.clearThroat = function() { 
        return "Ahem";
    };

    that.getName = function() {
        return spec.name;
    };

    that.says = function() {
        return my.clearThroat() + ' ' + spec.saying || '';
    };

    return that;
};

var cat = function(spec, my) {
    var that = {};
    my = my || {};

    spec.saying = spec.saying || 'meow';
    that = mammal(spec, my);

    that.purr = function() { 
        return my.clearThroat() + " purr"; 
    };

    that.getName = function() { 
        return that.says() + ' ' + spec.name + ' ' + that.says();
    };

    return that;
};

var kitty = cat({name: "Fluffy"});

我遇到的主要问题是，每次我制作

哺乳动物

或

猫

时，JavaScript解释器都必须重新编译其中的所有函数。也就是说，您不能在实例之间共享代码

---

我的问题是：如何使这段代码更高效？例如，如果我制作了数千个

cat

对象，那么修改此模式以利用

原型

对象的最佳方式是什么

好吧，如果你打算大量生产

哺乳动物

或

猫

，你就不能这样做。取而代之的是用老式的方式（原型）继承财产。您仍然可以按照上面的方法来构造构造函数，但是您可以使用隐式的

this

和一些表示基类的变量（在本例中，

this.demalator

），而不是

that

和

my

）

---

我会使用

my

以外的另一个名称作为基本访问，并将其存储在

this

中的

cat

构造函数中。在本例中，我使用了

哺乳动物

，但如果您希望静态访问全局

哺乳动物

对象，这可能不是最好的方法。另一个选项是命名变量

base

，如果您想要隐私并且不喜欢protyping，您可能喜欢也可能不喜欢这种方法：

（注意：它使用jQuery.extend）

var namespace=namespace | |{}；
//虚拟基类
namespace.base=函数（子，未定义）{
var base={instance:this}；
base.hierarchy=[]；
base.fn={
//检查base是否属于某个类（必须委派）
is：功能（CONTR）{
返回（this.hierarchy[this.hierarchy.length-1]==constr）；
},
//检查base是否扩展了某个类（必须委派）
继承：函数（constr）{
for（var i=0；i

唯一的缺点是，由于隐私范围，您只能扩展虚拟类，而不能扩展实例类

下面是我如何扩展namespace.base以绑定/取消绑定/触发自定义事件的示例

// virtual base class for controls
namespace.controls.base = function (sub) {

    var base = { instance: this };

    base.keys = {
        unknown: 0,
        backspace: 8,
        tab: 9,
        enter: 13,
        esc: 27,
        arrowUp: 38,
        arrowDown: 40,
        f5: 116
    }

    base.fn = {

        // bind/unbind custom events. (has to be called via delegate)
        listeners: {

            // bind custom event
            bind: function (type, fn) {

                if (fn != undefined) {

                    if (this.listeners[type] == undefined) {
                        throw (this.type + ': event type \'' + type + '\' is not supported');
                    }

                    this.listeners[type].push(fn);
                }

                return this;
            },

            // unbind custom event
            unbind: function (type) {

                if (this.listeners[type] == undefined) {
                    throw (this.type + ': event type \'' + type + '\' is not supported');
                }

                this.listeners[type] = [];

                return this;
            },

            // fire a custom event
            fire: function (type, e) {

                if (this.listeners[type] == undefined) {
                    throw (this.type + ': event type \'' + type + '\' does not exist');
                }

                for (var i = 0; i < this.listeners[type].length; i++) {

                    this.listeners[type][i](e);
                }

                if(e != undefined) e.stopPropagation();
            }
        }
    };

    base.public = {
        bind: base.fn.listeners.bind,
        unbind: base.fn.listeners.unbind
    };

    base = new namespace.base(base);

    base.fire = base.fn.delegate(base, base.fn.listeners.fire);

    return base.extend(sub);
};

//控件的虚拟基类
namespace.controls.base=函数（子）{
var base={instance:this}；
base.keys={
未知：0，
退格：8，
表9：，
输入：13，
esc:27，
截至：38，
向下箭头：40，
f5:116
}
base.fn={
//绑定/取消绑定自定义事件。（必须通过委托调用）
听众：{
//绑定自定义事件
绑定：函数（类型，fn）{
如果（fn！=未定义）{
if（this.listeners[type]==未定义）{
抛出（this.type+'：不支持事件类型\'+'type+'\'）；
}
this.listeners[type].push（fn）；
}
归还这个；
},
//解除绑定自定义事件
解除绑定：函数（类型）{
if（this.listeners[type]==未定义）{
抛出（this.type+'：不支持事件类型\'+'type+'\'）；
}
this.listeners[type]=[]；
归还这个；
},
//触发自定义事件
火灾：功能（类型e）{
if（this.listeners[type]==未定义）{
抛出（this.type+'：事件类型\''+type+'\'不存在）；
}
对于（var i=0；i

让我向您介绍从未使用原型的经典继承。这是一个糟糕的编码练习，但会教给你真正的经典继承，它总是与原型继承相比较：

var namespace = namespace || {};

// virtual base class
namespace.base = function (sub, undefined) {

    var base = { instance: this };

    base.hierarchy = [];

    base.fn = {

        // check to see if base is of a certain class (must be delegated)
        is: function (constr) {

            return (this.hierarchy[this.hierarchy.length - 1] === constr);
        },

        // check to see if base extends a certain class (must be delegated)
        inherits: function (constr) {

            for (var i = 0; i < this.hierarchy.length; i++) {

                if (this.hierarchy[i] == constr) return true;
            }
            return false;
        },

        // extend a base (must be delegated)
        extend: function (sub) {

            this.hierarchy.push(sub.instance.constructor);

            return $.extend(true, this, sub);
        },

        // delegate a function to a certain context
        delegate: function (context, fn) {

            return function () { return fn.apply(context, arguments); }
        },

        // delegate a collection of functions to a certain context
        delegates: function (context, obj) {

            var delegates = {};

            for (var fn in obj) {

                delegates[fn] = base.fn.delegate(context, obj[fn]);
            }

            return delegates;
        }
    };

    base.public = {
        is: base.fn.is,
        inherits: base.fn.inherits
    };

    // extend a sub-base
    base.extend = base.fn.delegate(base, base.fn.extend);

    return base.extend(sub);
};

namespace.MyClass = function (params) {

    var base = { instance: this };

    base.vars = {
        myVar: "sometext"
    }

    base.fn = {
        init: function () {

            base.vars.myVar = params.myVar;
        },

        alertMyVar: function() {

            alert(base.vars.myVar);
        }

    };

    base.public = {
        alertMyVar: base.fn.alertMyVar
    };

    base = namespace.base(base);

    base.fn.init();

    return base.fn.delegates(base,base.public);
};

newMyClass = new namespace.MyClass({myVar: 'some text to alert'});
newMyClass.alertMyVar();

// virtual base class for controls
namespace.controls.base = function (sub) {

    var base = { instance: this };

    base.keys = {
        unknown: 0,
        backspace: 8,
        tab: 9,
        enter: 13,
        esc: 27,
        arrowUp: 38,
        arrowDown: 40,
        f5: 116
    }

    base.fn = {

        // bind/unbind custom events. (has to be called via delegate)
        listeners: {

            // bind custom event
            bind: function (type, fn) {

                if (fn != undefined) {

                    if (this.listeners[type] == undefined) {
                        throw (this.type + ': event type \'' + type + '\' is not supported');
                    }

                    this.listeners[type].push(fn);
                }

                return this;
            },

            // unbind custom event
            unbind: function (type) {

                if (this.listeners[type] == undefined) {
                    throw (this.type + ': event type \'' + type + '\' is not supported');
                }

                this.listeners[type] = [];

                return this;
            },

            // fire a custom event
            fire: function (type, e) {

                if (this.listeners[type] == undefined) {
                    throw (this.type + ': event type \'' + type + '\' does not exist');
                }

                for (var i = 0; i < this.listeners[type].length; i++) {

                    this.listeners[type][i](e);
                }

                if(e != undefined) e.stopPropagation();
            }
        }
    };

    base.public = {
        bind: base.fn.listeners.bind,
        unbind: base.fn.listeners.unbind
    };

    base = new namespace.base(base);

    base.fire = base.fn.delegate(base, base.fn.listeners.fire);

    return base.extend(sub);
};

function Person(name, age){
  this.name = name;
  this.age = age;
  this.sayHello = function(){return "Hello! this is " + this.name;}
}

function Student(name, age, grade){
  Person.apply(this, [name, age]);
  this.grade = grade
}

var pete = new Student('Pete', 7, 1);

function Person(name, age){
  this.name = name;
  this.age = age;
  this.sayHello = function(){
    return "Hello! this is " + this.name + ". I am " this.age + " years old";
  }
}

  var Mammal = function (spec) {
    this.spec = spec;
}.define({
    clearThroat: function () { return "Ahem" },
    getName: function () {
        return this.spec.name;
    },
    says: function () {
        return this.clearThroat() + ' ' + spec.saying || '';
    }
});

var Cat = Mammal.inheritWith(function (base, baseCtor) {
    return {
        constructor: function(spec) { 
            spec = spec || {};
            baseCtor.call(this, spec); 
        },
        purr: function() {
            return this.clearThroat() + " purr";
        },
        getName: function() {
            return this.says() + ' ' + this.spec.name + this.says();
        }
    }
});

var kitty = new Cat({ name: "Fluffy" });
kitty.purr(); // Ahem purr
kitty.getName(); // Ahem Fluffy Ahem

var Mammal = function (spec) {
    this.spec = spec;
}.define({
    clearThroat: function () { return "Ahem" },
    getName: function () {
        return this.spec.name;
    },
    says: function () {
        return this.clearThroat() + ' ' + spec.saying || '';
    }
});

var Cat = Mammal.fastClass(function (base, baseCtor) {
    return function() {
        this.constructor = function(spec) { 
            spec = spec || {};
            baseCtor.call(this, spec); 
        };
        this.purr = function() {
            return this.clearThroat() + " purr";
        },
        this.getName = function() {
            return this.says() + ' ' + this.spec.name + this.says();
        }
    }
});

var kitty = new Cat({ name: "Fluffy" });
kitty.purr(); // Ahem purr
kitty.getName(); // Ahem Fluffy Ahem

Function.prototype.fastClass = function (creator) {
    var baseClass = this, ctor = (creator || function () { this.constructor = function () { baseClass.apply(this, arguments); } })(this.prototype, this)

    var derrivedProrotype = new ctor();

    if (!derrivedProrotype.hasOwnProperty("constructor"))
        derrivedProrotype.constructor = function () { baseClass.apply(this, arguments); }

    derrivedProrotype.constructor.prototype = derrivedProrotype;
    return derrivedProrotype.constructor;
};

Function.prototype.inheritWith = function (creator, makeConstructorNotEnumerable) {
    var baseCtor = this;
    var creatorResult = creator.call(this, this.prototype, this) || {};
    var Derrived = creatorResult.constructor ||
    function defaultCtor() {
        baseCtor.apply(this, arguments);
    }; 
    var derrivedPrototype;
    function __() { };
    __.prototype = this.prototype;
    Derrived.prototype = derrivedPrototype = new __;

    for (var p in creatorResult)
        derrivedPrototype[p] = creatorResult[p];

    if (makeConstructorNotEnumerable && canDefineNonEnumerableProperty) //this is not default as it carries over some performance overhead
        Object.defineProperty(derrivedPrototype, 'constructor', {
            enumerable: false,
            value: Derrived
        });

    return Derrived;
};

Function.prototype.define = function (prototype) {
    var extendeePrototype = this.prototype;
    if (prototype)
        for (var p in prototype)
            extendeePrototype[p] = prototype[p];
    return this;
}