使用Commandline设计模式之前的源代码：
<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 work uploadAPI = { "name": "ActiveX"}; } else if( isHTML5Supported()) { // lots of initialization work uploadAPI = { "name": "HTML5"}; } else if( isFlashSupported()) { // lots of initialization work uploadAPI = { "name": "Flash"}; } else { // lots of initialization work uploadAPI = { "name": "Form"}; } console.log(uploadAPI); </script> </html>
我们可以使用CommandLine设计模式，将这些冗长的IF-ELSE语句消除：
commandline命令行模式的JavaScript实现版本：
<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 work a(); return { "name": "ActiveX"}; } catch (e) { // user broswer does not support ActiveX return null; } } var getHTML5 = function() { try { // lots of initialization work return { "name": "HTML5"}; } catch (e) { // user broswer does not support HTML5 return null; } } var getFlash = function() { try { // lots of initialization work return { "name": "Flash"}; } catch (e) { // user broswer does not support Flash return null; } } var getForm = function() { return { "name": "Form"}; } var uploadAPI = getActiveX.after(getHTML5).after(getFlash).after(getForm)(); console.log(uploadAPI); </script> </html>
