鉴于此代码:
// Constructor.
var Interface = function (name, methods) {
if (arguments.length != 2) {
throw new Error("Interface constructor called with " + arguments.length + "arguments, but expected exactly 2.");
}
this.name = name;
this.methods = [];
for (var i = 0, len = methods.length; i < len; i++) {
if (typeof methods[i] !== 'string') {
throw new Error("Interface constructor expects method names to be " + "passed in as a string.");
}
this.methods.push(methods[i]);
}
};
// Static class method.
Interface.ensureImplements = function (object) {
if (arguments.length < 2) {
throw new Error("Function Interface.ensureImplements called with " + arguments.length + "arguments, but expected at least 2.");
}
for (var i = 1, len = arguments.length; i < len; i++) {
var interface = arguments[i];
if (interface.constructor !== Interface) {
throw new Error("Function Interface.ensureImplements expects arguments" + "two and above to be instances of Interface.");
}
for (var j = 0, methodsLen = interface.methods.length; j < methodsLen; j++) {
var method = interface.methods[j];
if (!object[method] || typeof object[method] !== 'function') {
throw new Error("Function Interface.ensureImplements: object " + "does not implement the " + interface.name + " interface. Method " + method + " was not found.");
}
}
}
};
function extend( a, b ){
for( var key in b )
if( b.hasOwnProperty(key) )
a[key] = b[key];
return a;
}
var Macbook = new Interface( "Macbook",
["addEngraving",
"addParallels",
"add4GBRam",
"add8GBRam",
"addCase"]); /* Returns an object that stores the name of the Interface and the array of methods (pushed) */
// A Macbook Pro might thus be represented as follows:
var MacbookPro = function(){
// implements Macbook
};
MacbookPro.prototype = {
addEngraving: function(){
},
addParallels: function(){
},
add4GBRam: function(){
},
add8GBRam:function(){
},
addCase: function(){
},
getPrice: function(){
// Base price
return 900.00;
}
};
var MacbookDecorator = function( macbook ){
Interface.ensureImplements( macbook, Macbook );
this.macbook = macbook;
};
MacbookDecorator.prototype = {
addEngraving: function(){
return this.macbook.addEngraving();
},
addParallels: function(){
return this.macbook.addParallels();
},
add4GBRam: function(){
return this.macbook.add4GBRam();
},
add8GBRam:function(){
return this.macbook.add8GBRam();
},
addCase: function(){
return this.macbook.addCase();
},
getPrice: function(){
return this.macbook.getPrice();
}
};
var CaseDecorator = function( macbook ){
this.macbook = macbook;
};
// Let's now extend (decorate) the CaseDecorator
// with a MacbookDecorator
extend( CaseDecorator, MacbookDecorator );
CaseDecorator.prototype.addCase = function(){
return this.macbook.addCase() + "Adding case to macbook";
};
CaseDecorator.prototype.getPrice = function(){
return this.macbook.getPrice() + 45.00;
};
var myMacbookPro = new MacbookPro();
// Outputs: 900.00
console.log( myMacbookPro.getPrice() );
// Decorate the macbook
var decoratedMacbookPro = new CaseDecorator( myMacbookPro );
// This will return 945.00
console.log( decoratedMacbookPro.getPrice() );
第一眼看上去对我很好。 然而,最近我更深入地分析了这段代码,并遇到了一些我今天想与大家分享的问题。 让我们开始吧: 此代码的当前版本包含此部分:
MacbookDecorator.prototype = {
addEngraving: function(){
return this.macbook.addEngraving();
},
addParallels: function(){
return this.macbook.addParallels();
},
add4GBRam: function(){
return this.macbook.add4GBRam();
},
add8GBRam:function(){
return this.macbook.add8GBRam();
},
addCase: function(){
return this.macbook.addCase();
},
getPrice: function(){
return this.macbook.getPrice();
}
};
在这一点上,它实际上没有意义(如果我错了就抓住我),尤其是当使用以下方式调用时:
var myMacbookPro = new MacbookPro();
// Outputs: 900.00
console.log( myMacbookPro.getPrice() );
// Decorate the macbook
var decoratedMacbookPro = new CaseDecorator( myMacbookPro );
// This will return 945.00
console.log( decoratedMacbookPro.getPrice() );
MacbookDecorator.prototype在给定的上下文中没有任何意义。 你们中的一些人可能会说它是链条的一部分,因此MacbookDecorator的原型有其“#”;放在那里。 但不是。 它在这里没有被称为实用的地方。 的为什么吗
extend( CaseDecorator, MacbookDecorator );
这可能有些人相信,这是魔法发生的部分,但是要记住这一点:
function extend( a, b ){
for( var key in b )
if( b.hasOwnProperty(key) )
a[key] = b[key];
return a;
}
MacBookDecorator没有对CaseDecorator进行继承,事实上,这种方式的原型被完全忽略,而不是由CaseDecorator继承。 另外,extend函数根本没有用,因为它只读取对象的属性,但是提供的两个参数都是函数,因此,如果函数至少在执行之前没有执行,则不会继承任何继承。 ,这很棘手,因为此时甚至没有定义.macbook。
这是我的代码版本,实际上做的完全相同,省略了不必要的,部分非常刺激的部分:
// Constructor.
var Interface = function (name, methods) {
if (arguments.length != 2) {
throw new Error("Interface constructor called with " + arguments.length + "arguments, but expected exactly 2.");
}
this.name = name;
this.methods = [];
for (var i = 0, len = methods.length; i < len; i++) {
if (typeof methods[i] !== 'string') {
throw new Error("Interface constructor expects method names to be " + "passed in as a string.");
}
this.methods.push(methods[i]);
}
};
// Static class method.
Interface.ensureImplements = function (object) {
if (arguments.length < 2) {
throw new Error("Function Interface.ensureImplements called with " + arguments.length + "arguments, but expected at least 2.");
}
for (var i = 1, len = arguments.length; i < len; i++) {
var interface = arguments[i];
if (interface.constructor !== Interface) {
throw new Error("Function Interface.ensureImplements expects arguments" + "two and above to be instances of Interface.");
}
for (var j = 0, methodsLen = interface.methods.length; j < methodsLen; j++) {
var method = interface.methods[j];
if (!object[method] || typeof object[method] !== 'function') {
throw new Error("Function Interface.ensureImplements: object " + "does not implement the " + interface.name + " interface. Method " + method + " was not found.");
}
}
}
};
var Macbook = new Interface( "Macbook",
["addEngraving",
"addParallels",
"add4GBRam",
"add8GBRam",
"addCase"]); /* Gives back an object that stores the name of the Interface and the array of methods (pushed) */
// A Macbook Pro might thus be represented as follows:
var MacbookPro = function(){};
var decorator = function() {
return {
addEngraving: function(){
},
addParallels: function(){
},
add4GBRam: function(){
},
add8GBRam:function(){
},
addCase: function(){
},
getPrice: function(){
// Base price
return 900.00;
}
}
}
MacbookPro.prototype = decorator();
//var MacbookDecorator = function( macbook ){
// Interface.ensureImplements( macbook, Macbook );
// this.macbook = macbook;
//}
/*MacbookDecorator.prototype = decorator();*/
var CaseDecorator = function( macbook ){
this.macbook = macbook;
};
CaseDecorator.prototype.addCase = function(){
return this.macbook.addCase() + "Adding case to macbook";
};
CaseDecorator.prototype.getPrice = function(){
return this.macbook.getPrice() + 45.00;
};
// Decorate the macbook
var decoratedMacbookPro = new CaseDecorator( new MacbookPro() );
// This will return 945.00
console.log( decoratedMacbookPro.getPrice() );
您如何看待这一点,作者是否遗漏了某些内容,或者这是真的吗?
答案 0 :(得分:1)
extend( CaseDecorator, MacbookDecorator );
MacBookDecorator没有对CaseDecorator进行继承,实际上,这种方式的原型被完全忽略,而不是由CaseDecorator继承。
你对此完全正确。这对我来说似乎是作者的失误,实际上应该是
extend(CaseDecorator.prototype, MacbookDecorator.prototype);
甚至是完整的原型继承设置。
extend
只会读取对象的属性,但提供的两个参数都是函数
不要忘记函数也是对象,因此如果它们只有自己的属性,extend
就可以对它们做很多事情。但是你是对的,在这种情况下它什么都不做,因为像.prototype
或.name
这样的典型函数实例属性是不可枚举的。