用JavaScript实现的设计模式之commandline(命令行)模式

Jerry Wang

发布于 2020-03-19 17:28:41

4000

发布于 2020-03-19 17:28:41

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>

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原始发表：2020-03-18 ，如有侵权请联系 cloudcommunity@tencent.com 删除

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