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用JavaScript实现的设计模式之commandline(命令行)模式
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用JavaScript实现的设计模式之commandline(命令行)模式
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使用Commandline設計模式之前的源代碼：
<html> <script>// Priority: ActiveX > HTML5 > Flash > Form(default) function isActiveXSupported(){//...return false; }function isHTML5Supported(){//...return false; }function isFlashSupported(){//...return false; }var uploadAPI; if ( isActiveXSupported()) {// lots of initialization workuploadAPI = { "name": "ActiveX"}; } else if( isHTML5Supported()) {// lots of initialization workuploadAPI = { "name": "HTML5"}; } else if( isFlashSupported()) {// lots of initialization workuploadAPI = { "name": "Flash"}; } else {// lots of initialization workuploadAPI = { "name": "Form"}; }console.log(uploadAPI);</script> </html>我們可以使用CommandLine設計模式，將這些冗長的IF-ELSE語句消除：
commandline命令行模式的JavaScript實現版本：
<html> <script>Function.prototype.after = function( func ){var _self = this;return function() {var ret = _self.apply( this, arguments );if ( ret ) {return ret;}return func.apply( this, arguments);} }// Priority: ActiveX > HTML5 > Flash > Form(default) var getActiveX = function() {try {// lots of initialization worka();return { "name": "ActiveX"};}catch (e) {// user broswer does not support ActiveXreturn null;} }var getHTML5 = function() {try {// lots of initialization workreturn { "name": "HTML5"};}catch (e) {// user broswer does not support HTML5return null;} }var getFlash = function() {try {// lots of initialization workreturn { "name": "Flash"};}catch (e) {// user broswer does not support Flashreturn null;} }var getForm = function() {return { "name": "Form"}; }var uploadAPI = getActiveX.after(getHTML5).after(getFlash).after(getForm)();console.log(uploadAPI);</script> </html>總結
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