Pro Javascript Design Patterns勘误Errata汇总，持续更新中
结合从网上搜集的资料，现将Pro Javascript Design Patterns一书几处有错误嫌疑的地方整理出来。
1. P.28: Chapter 3： Encapsulation and Information Hiding > Fully Exposed Object 错误类型：印刷错误+计算方法错误
原代码为：
Book.prototype = {
checkIsbn: function(isbn) {
if(isbn == undefined || typeof isbn != 'string') {
return false;
}
isbn = isbn.replace(/-/. ''); // Remove dashes.
if(isbn.length != 10 && isbn.length != 13) {
return false;
}
var sum = 0;
if(isbn.length === 10) { // 10 digit ISBN.
If(!isbn.match(\^\d{9}\)) { // Ensure characters 1 through 9 are digits.
return false;
}
var sum = 0;
if (isbn.length === 10) {
console.log("checking for 10...");
if (!isbn.match(/^\d{9}/)) {
return false;
}
for ( var i = 0; i < 9; i++) {
sum += isbn.charAt(i) * (10 - i);
}
var checksum = sum % 11;
checksum = (checksum === 10) ? "X" : checksum;
if (isbn.charAt(9) != checksum) {
return false;
}
} else {
if (!isbn.match(/^\d{12}/)) {
return false;
}
for ( var i = 0; i < 12; i++) {
sum += isbn.charAt(i) * ((i % 2 === 0) ? 1 : 3);
}
var checksum = sum % 10;
if (isbn.charAt(12) != checksum) {
return false;
}
}
...
};应更正为：
Book.prototype = {
checkIsbn: function(isbn) {
if(isbn == undefined || typeof isbn != 'string') {
return false;
}
isbn = isbn.replace(/-/g, ''); // Remove dashes.
if(isbn.length != 10 && isbn.length != 13) {
return false;
}
var sum = 0;
if(isbn.length === 10) { // 10 digit ISBN.
if(!isbn.match(\^\d{9}\)) { // Ensure characters 1 through 9 are digits.
return false;
}
var sum = 0;
if(isbn.length === 10) { // 10 digit ISBN.
If(!isbn.match(\^\d{9}\)) { // Ensure characters 1 through 9 are digits.
return false;
} var sum = 0; if (isbn.length === 10) { console.log("checking for 10..."); if (!isbn.match(/^\d{9}/)) { return false; } for ( var i = 0; i < 9; i++) { sum += isbn.charAt(i) * (10 - i); } var checksum = (11 - sum % 11) % 11; checksum = (checksum === 10) ? "X" : checksum; if (isbn.charAt(9) != checksum) { return false; } } else { if (!isbn.match(/^\d{12}/)) { return false; } for ( var i = 0; i < 12; i++) { sum += isbn.charAt(i) * ((i % 2 === 0) ? 1 : 3); } var checksum = (10 - sum % 10) % 10; if (isbn.charAt(12) != checksum) { return false; } }
...
};
关于验证ISBN号的正确计算方法，我参考了维基百科上的International Standard Book Number。这一点作者太疏忽大意了。
2. P.38: Chapter 3： Encapsulation and Information Hiding > Constants 错误类型：印刷错误+结构错误
原代码为：
var Class = (function() {
// Constants (created as private static attributes).
var UPPER_BOUND = 100;
// Privileged static method.
this.getUPPER_BOUND() {
return UPPER_BOUND;
}
...
// Return the constructor.
return function(constructorArgument) {
...
}
})();
/* Grouping constants together. */
var Class = (function() {
// Private static attributes.
var constants = {
UPPER_BOUND: 100,
LOWER_BOUND: -100
}
// Privileged static method.
this.getConstant(name) {
return constants[name];
}
...
// Return the constructor.
return function(constructorArgument) {
...
}
})();
/* Usage. */
Class.getConstant('UPPER_BOUND');
应更正为：
var Class = (function() {
// Constants (created as private static attributes).
var UPPER_BOUND = 100;
// Privileged static method.
this.getUPPER_BOUND=function() {
return UPPER_BOUND;
}
...
// Return the constructor.
return function(constructorArgument) {
...
}
})();
/* Grouping constants together. */
var Class = (function() {
// Private static attributes.
var constants = {
UPPER_BOUND: 100,
LOWER_BOUND: -100
}
// Privileged static method.
this.getConstant=function(name) {
return constants[name];
}
...
// Return the constructor.
return function(constructorArgument) {
...
}
})();
/* Usage. */
Class.getConstant('UPPER_BOUND');
关于此处代码的运行，有人提出并不能达到作者所提出的需求，因为即使照上面的方法更正后，由于this.getUPPER_BOUND和this.getConstant都是在自执行函数的内部运行，这里的this实际上将指向全局变量，即window。在StacksOverflow上，有人提出此讨论，众人相继给出解决办法，敬请参阅原文。
3. P.89: Chapter 6： Chaining > Using Callbacks to Retrieve Data from Chained Methods 错误类型：印刷错误+结构错误
原代码为：
// Accessor without function callbacks: returning requested data in accessors.
window.API = window.API || {};
API.prototype = function() {
var name = 'Hello world';
// Privileged mutator method.
setName: function(newName) {
name = newName;
return this;
},
// Privileged accessor method.
getName: function() {
return name;
}
}();
// Implementation code.
var o = new API;
console.log(o.getName()); // Displays 'Hello world'.
console.log(o.setName('Meow').getName()); // Displays 'Meow'.
// Accessor with function callbacks.
window.API2 = window.API2 || {};
API2.prototype = function() {
var name = 'Hello world';
// Privileged mutator method.
setName: function(newName) {
name = newName;
return this;
},
// Privileged accessor method.
getName: function(callback) {
callback.call(this, name);
return this;
}
}();
// Implementation code.
var o2 = new API2;
o2.getName(console.log).setName('Meow').getName(console.log);
// Displays 'Hello world' and then 'Meow'.
应更正为：
// Accessor without function callbacks: returning requested data in accessors.
window.API = window.API || function(){};
API.prototype = function() {
var name = 'Hello world';
return {
// Privileged mutator method.
setName: function(newName) {
name = newName;
return this;
},
// Privileged accessor method.
getName: function() {
return name;
}
}
}();
// Implementation code.
var o = new API;
console.log(o.getName()); // Displays 'Hello world'.
console.log(o.setName('Meow').getName()); // Displays 'Meow'.
// Accessor with function callbacks.
window.API2 = window.API2 || function(){};
API2.prototype = function() {
var name = 'Hello world';
return {// Privileged mutator method.
setName: function(newName) {
name = newName;
return this;
},
// Privileged accessor method.
getName: function(callback) {
callback.call(this, name);
return this;
}
}
}();
// Implementation code.
var o2 = new API2;
o2.getName(console.log).setName('Meow').getName(console.log);
// Displays 'Hello world' and then 'Meow'.这个问题是http://www.apress.com/9781590599082/上有人提出的。
4. P.100: Chapter 7: The Factory Pattern > XHR Factory 错误类型：印刷错误?结构错误?
原代码为：
/* SimpleHandler class. */
var SimpleHandler = function() {}; // implements AjaxHandler
SimpleHandler.prototype = {
request: function(method, url, callback, postVars) {
...
},
createXhrObject: function() { // Factory method.
var methods = [
function() { return new XMLHttpRequest(); },
function() { return new ActiveXObject('Msxml2.XMLHTTP'); },
function() { return new ActiveXObject('Microsoft.XMLHTTP'); }
];
for(var i = 0, len = methods.length; i < len; i++) {
try {
methods[i]();
}
catch(e) {
continue;
}
// If we reach this point, method[i] worked.
this.createXhrObject = methods[i]; // Memoize the method.
return methods[i];
}
// If we reach this point, none of the methods worked.
throw new Error('SimpleHandler: Could not create an XHR object.');
}
};
应更正为：
/* SimpleHandler class. */
var SimpleHandler = function() {}; // implements AjaxHandler
SimpleHandler.prototype = {
request: function(method, url, callback, postVars) {
...
},
createXhrObject: function() { // Factory method.
var methods = [
function() { return new XMLHttpRequest(); },
function() { return new ActiveXObject('Msxml2.XMLHTTP'); },
function() { return new ActiveXObject('Microsoft.XMLHTTP'); }
];
for(var i = 0, len = methods.length; i < len; i++) {
try {
methods[i]();
}
catch(e) {
continue;
}
// If we reach this point, method[i] worked.
this.createXhrObject = methods[i]; // Memoize the method.
return methods[i]();
}
// If we reach this point, none of the methods worked.
throw new Error('SimpleHandler: Could not create an XHR object.');
}
};
这一错误很可能是作者没有测试代码，照书中所述，createXhrObject要在第一次运行之后记住当前的运行环境中能够使用的HttpRequest对象，methods数组中的对象为函数，因此要用一个括号执行后才能得到真正的对象。
5. P.130: Chapter 9: The Composite Pattern > Form Validation 错误类型：印刷错误
原代码为：
/* Field class, abstract. */
var Field = function(id) { // implements Composite, FormItem
this.id = id;
this.element;
};
...
Field.prototype.save = function() {
setCookie(this.id, this.getValue);
};
应更正为：
/* Field class, abstract. */
var Field = function(id) { // implements Composite, FormItem
this.id = id;
this.element;
};
...
Field.prototype.save = function() {
setCookie(this.id, this.getValue());
};
6. P.155: Chapter 11: The Adapter Pattern > Adapting an Email API 错误类型：印刷错误
原代码为：
// dedMail application interface.
var dedMail = (function() {
function request(id, type, callback) {
...
}
return {
...
formatMessage: function(e) {
var e = e || window.event;
try {
e.preventDefault();
}
catch(ex) {
e.returnValue = false;
}
var targetEl = e.target || e.srcElement;
var id = targetEl.id.toString().split('-')[1];
dedMail.getMail(id, function(msgObject) {
var resp = eval('('+msgObject+')');
...
messagePane.innerHTML = DED.util.substitute(details, resp);
}
};
})(); // Set up mail implementation.
addEvent(window, 'load', function() {
var threads = getElementsByClass('thread', 'a');
var messagePane = $('message-pane');
for (var i=0, len=threads.length; formatMessage );
}
});
应更正为：
// dedMail application interface.
var dedMail = (function() {
function request(id, type, callback) {
...
}
return {
...
formatMessage: function(e) {
var e = e || window.event;
try {
e.preventDefault();
}
catch(ex) {
e.returnValue = false;
}
var targetEl = e.target || e.srcElement;
var id = targetEl.id.toString().split('-')[1];
dedMail.getMail(id, function(msgObject) {
var resp = eval('('+msgObject+')');
...
messagePane.innerHTML = DED.util.substitute(details, resp);
})
}
};
})(); // Set up mail implementation.
addEvent(window, 'load', function() {
var threads = getElementsByClass('thread', 'a');
var messagePane = $('message-pane');
for (var i=0, len=threads.length; dedMail.formatMessage );
}
});
7. P.161,162,165,166: Chapter 12: The Decorator Pattern > The Structure of the Decorator 错误类型：结构错误
在多个页码处均为同一错误类型，仅举其中一处为例。P.161:
原代码为：
/* HeadlightDecorator class. */
var HeadlightDecorator = function(bicycle) { // implements Bicycle
this.superclass.constructor(bicycle); // Call the superclass's constructor.
}
extend(HeadlightDecorator, BicycleDecorator); // Extend the superclass.
HeadlightDecorator.prototype.assemble = function() {
return this.bicycle.assemble() + ' Attach headlight to handlebars.';
};
HeadlightDecorator.prototype.getPrice = function() {
return this.bicycle.getPrice() + 15.00;
};
应更正为：
/* HeadlightDecorator class. */
var HeadlightDecorator = function(bicycle) { // implements Bicycle
HeadlightDecorator.superclass.constructor.call(this, bicycle); // Call the superclass's constructor.
}
extend(HeadlightDecorator, BicycleDecorator); // Extend the superclass.
HeadlightDecorator.prototype.assemble = function() {
return this.bicycle.assemble() + ' Attach headlight to handlebars.';
};
HeadlightDecorator.prototype.getPrice = function() {
return this.bicycle.getPrice() + 15.00;
};
8. P.191: Chapter 13: The Flyweight Pattern > Sotring Instances for Later Reuse 错误类型：结构错误
原代码为：
var DialogBoxManager = (function() {
var created = [];
return {
displayDialogBox : function(id, header, body, footer) {
var inUse = this.numberInUse();
if (inUse > created.length) {
created.push(this.createDialogBox(id));
}
created[i].show(header, body, footer);
},
createDialogBox : function(id) {
return new DialogBox(id);
},
numberInUse : function() {
var inUse = 0;
for ( var i = 0; i < created.length; ++i) {
console.log(created[i].state());
if (created[i].state() == "visible") {
inUse++;
}
}
return inUse;
}
}
})();
应更正为：
var DialogBoxManager = (function() {
var created = [];
return {
displayDialogBox : function(header, body, footer) {
(this.getFirstHiddenDialogBox() || this.createDialogBox()).show(header, body, footer);
},
createDialogBox : function() {
var db = new DialogBox(this.numberInUse());
created.push(db);
return db;
},
getFirstHiddenDialogBox : function() {
for ( var i = 0; i < created.length; ++i) {
if (created[i].state() != "visible") {
return created[i];
}
continue;
}
return null;
}, numberInUse : function() {
var inUse = 0;
for ( var i = 0; i < created.length; ++i) {
if (created[i].state() == "visible") {
inUse++;
}
}
return inUse;
}
}
})();
原代码中inUse > created.length是显然行不通的，inUse永远也不可能大于created.length，其判断也就失去了意义。改进后的代码将能在调用自动displayDialogBox时判断是否有隐藏的已经建立的DialogBox，如果有即用之，如果没有即调用createDialogBox创建一个新的，numberInUse在createDialogBox函数中使用。
9. P.198, P.248, P.252: Chapter 14: The Proxy Pattern > The Structure of the Proxy; Chapter 17: The Chain of Responsibility > The Structure of the Chain of Responsibility 错误类型：印刷错误
两处文字中均少了book，导致程序运行出现错误。
原代码为：
PublicLibrary.prototype = {
findBooks : function(searchString) {
var results = [];
for ( var isbn in this.catalog) {
if (!this.catalog.hasOwnProperty(isbn)) {
continue;
}
if (this.catalog[isbn].getTitle().match(searchString)
|| this.catalog[isbn].getAuthor().match(searchString)) {
results.push(this.catalog[isbn]);
}
}
return results;
}
...
addBook : function(newBook) {
this.catalog[newBook.getIsbn()] = {
book : newBook,
available : true
};
}
}
应更正为：
PublicLibrary.prototype = {
findBooks : function(searchString) {
var results = [];
for ( var isbn in this.catalog) {
if (!this.catalog.hasOwnProperty(isbn)) {
continue;
}
if (this.catalog[isbn].book.getTitle().match(searchString)
|| this.catalog[isbn].book.getAuthor().match(searchString)) {
results.push(this.catalog[isbn].book);
}
}
return results;
}
...
addBook : function(newBook) {
this.catalog[newBook.getIsbn()] = {
book : newBook,
available : true
};
}
}
10. P.250, P.254: Chapter 17: The Chain of Responsibility > The Structure of the Chain of Responsibility 错误类型：结构错误
原代码为：
var SciFiCatalog = function() {};// Implements Catalog
extend(SciFiCatalog , GenreCatalog);
应更正为：
var SciFiCatalog = function() {// Implements Catalog
SciFiCatalog.superclass.contructor.apply(this,arguments);
};
extend(SciFiCatalog , GenreCatalog);
Why?因为作者在本书中一直在用的extend方法是不能继承“父类”的constructor中的属性的，所以必须在“子类”的constructor中调用一遍该函数，以便“子类”继承“父类”的这些属性。
11. P.253: Chapter 17: The Chain of Responsibility > The Structure of the Chain of Responsibility 错误类型：印刷错误
原代码为：
if (found) {
outerloop: for ( var i = 0; i != this.catalog.length; ++i) {
var book = this.catalog[i];
if (book.getTitle().match(searchString)
|| book.getAuthor().match(searchString)) {
for ( var j = 0; j != request.results.length; ++j) {
if (request.results[j].getIsbn() === book.getIsbn()) {
continue outerloop;
}
}
request.results.push(book);
}
}
}
应更正为：
if (found) {
outerloop: for ( var i = 0; i != this.catalog.length; ++i) {
var book = this.catalog[i];
if (book.getTitle().match( request.searchString)
|| book.getAuthor().match( request.searchString)) {
for ( var j = 0; j != request.results.length; ++j) {
if (request.results[j].getIsbn() === book.getIsbn()) {
continue outerloop;
}
}
request.results.push(book);
}
}
}
这里的searchString前面显然是少了request，不然就是一个未定义的变量。
12. P.260: Chapter 17: The Chain of Responsibility > Adding Tags to Photos 错误类型：结构错误
原代码为：
DynamicGallery.prototype = {
...
getAllLeaves: function() {
var leaves = [];
for(var node, i = 0; node = this.getChild(i); i++) {
leaves.concat(node.getAllLeaves());
}
return leaves;
},
...
for(var results = [], node, i = 0; node = this.getChild(i); i++) {
results.concat(node.getPhotosWithTag(tag));
}
return results;
},
...
};
应更正为：
DynamicGallery.prototype = {
...
getAllLeaves: function() {
var leaves = [];
for(var node, i = 0; node = this.getChild(i); i++) {
leaves=leaves.concat(node.getAllLeaves());
}
return leaves;
},
...
for(var results = [], node, i = 0; node = this.getChild(i); i++) {
results=results.concat(node.getPhotosWithTag(tag));
}
return results;
},
...
};
Javascript中的Array.concat是在不改变原数组的情况下返回一个新数组。
本文来自http://www.cnblogs.com/pinocchioatbeijing/archive/2012/02/01/2334126.html，转载请注明，并欢迎大家不吝赐教。
- 上一篇 »JAVA项目工具包集合
- 下一篇 »JAVA中线程同步的方法，4种汇总