使用AmplifyJS和JQuery编写更好更优雅的javascript事件处理代码

标签：javascript事件处理   jquery事件处理   javascript发布订阅模式   

事件(或消息)是一种常用的软件设计模式，能够降低消息处理者和消息发布者的之间的耦合，比如J2EE里面的JMS规范。设计模式中的观察者模式(也叫发布/订阅模式)，这对于javascript代码同样适用。之前写的JQuery相关博客中，详细介绍了JQuery的事件处理机制和特性，具体可以参考这个目录下的文章。

JQuery事件处理其实就是使用了发布/订阅模式，包括它提供的命名空间机制、自定义事件都非常的棒，但是JQuery事件处理有一个缺陷：JQuery事件都是和DOM元素相关的，但是很多时候我们并不需要DOM元素，只希望使用事件的发布/订阅这种机制。

代码1：如果某个DOM元素不存在，那么不能依靠它使用事件的发布和订阅。

// not-exsit不存在的dom元素,事件处理无效
 $("not-exsit").bind("self-event",function(){alert(11);});
 $("not-exsit").trigger("self-event");

// 报异常$.trigger is not a function
  $.bind("self-event",function(){alert(11);});
  $.trigger("self-event");

<script src="amplify.js"></script>
<script>
	amplify.subscribe( "self-event", function(context){
		console.log("priority=5,data="+JSON.stringify(context));
	}, 5);
	
	
	amplify.subscribe( "self-event", function(context){
		console.log("priority=6,data="+JSON.stringify(context));
	}, 6); 
  
	amplify.subscribe( "self-event", function(context){
		console.log("priority=3,data="+JSON.stringify(context));
	}, 3);
  
  
  amplify.publish("self-event",{data:11});
  
</script>

下面附上AmplifyJS的源码amplify.core.js，可以看到源码非常的简短，也很容易看懂。

/*!
 * Amplify Core 1.1.2
 *
 * Copyright 2011 - 2013 appendTo LLC. (http://appendto.com/team)
 * Dual licensed under the MIT or GPL licenses.
 * http://appendto.com/open-source-licenses
 *
 * http://amplifyjs.com
 */
(function( global, undefined ) {

var slice = [].slice,
	subscriptions = {};

var amplify = global.amplify = {
	publish: function( topic ) {
		if ( typeof topic !== "string" ) {
			throw new Error( "You must provide a valid topic to publish." );
		}

		var args = slice.call( arguments, 1 ),
			topicSubscriptions,
			subscription,
			length,
			i = 0,
			ret;

		if ( !subscriptions[ topic ] ) {
			return true;
		}

		topicSubscriptions = subscriptions[ topic ].slice();
		for ( length = topicSubscriptions.length; i < length; i++ ) {
			subscription = topicSubscriptions[ i ];
			ret = subscription.callback.apply( subscription.context, args );
			if ( ret === false ) {
				break;
			}
		}
		return ret !== false;
	},

	subscribe: function( topic, context, callback, priority ) {
		if ( typeof topic !== "string" ) {
			throw new Error( "You must provide a valid topic to create a subscription." );
		}

		if ( arguments.length === 3 && typeof callback === "number" ) {
			priority = callback;
			callback = context;
			context = null;
		}
		if ( arguments.length === 2 ) {
			callback = context;
			context = null;
		}
		priority = priority || 10;

		var topicIndex = 0,
			topics = topic.split( /\s/ ),
			topicLength = topics.length,
			added;
		for ( ; topicIndex < topicLength; topicIndex++ ) {
			topic = topics[ topicIndex ];
			added = false;
			if ( !subscriptions[ topic ] ) {
				subscriptions[ topic ] = [];
			}

			var i = subscriptions[ topic ].length - 1,
				subscriptionInfo = {
					callback: callback,
					context: context,
					priority: priority
				};

			for ( ; i >= 0; i-- ) {
				if ( subscriptions[ topic ][ i ].priority <= priority ) {
					subscriptions[ topic ].splice( i + 1, 0, subscriptionInfo );
					added = true;
					break;
				}
			}

			if ( !added ) {
				subscriptions[ topic ].unshift( subscriptionInfo );
			}
		}

		return callback;
	},

	unsubscribe: function( topic, context, callback ) {
		if ( typeof topic !== "string" ) {
			throw new Error( "You must provide a valid topic to remove a subscription." );
		}

		if ( arguments.length === 2 ) {
			callback = context;
			context = null;
		}

		if ( !subscriptions[ topic ] ) {
			return;
		}

		var length = subscriptions[ topic ].length,
			i = 0;

		for ( ; i < length; i++ ) {
			if ( subscriptions[ topic ][ i ].callback === callback ) {
				if ( !context || subscriptions[ topic ][ i ].context === context ) {
					subscriptions[ topic ].splice( i, 1 );
					
					// Adjust counter and length for removed item
					i--;
					length--;
				}
			}
		}
	}
};

}( this ) );

更详细的API使用，可以参考下面这2篇文章：

AmplifyJS源码简析：事件分发

Extending Your jQuery Application with Amplify.js

使用AmplifyJS和JQuery编写更好更优雅的javascript事件处理代码

标签：javascript事件处理   jquery事件处理   javascript发布订阅模式   

原文地址：http://blog.csdn.net/aitangyong/article/details/46713253