aspect.js

define([], function(){

	// module:
	//		dojo/aspect

	"use strict";
	var undefined, nextId = 0;
	function advise(dispatcher, type, advice, receiveArguments){
		var previous = dispatcher[type];
		var around = type == "around";
		var signal;
		if(around){
			var advised = advice(function(){
				return previous.advice(this, arguments);
			});
			signal = {
				remove: function(){
					signal.cancelled = true;
				},
				advice: function(target, args){
					return signal.cancelled ?
						previous.advice(target, args) : // cancelled, skip to next one
						advised.apply(target, args);	// called the advised function
				}
			};
		}else{
			// create the remove handler
			signal = {
				remove: function(){
					if(this.advice){
						// remove the advice to signal that this signal has been removed
						this.advice = null;
						var previous = signal.previous;
						var next = signal.next;
						if(!next && !previous){
							delete dispatcher[type];
						}else{
							if(previous){
								previous.next = next;
							}else{
								dispatcher[type] = next;
							}
							if(next){
								next.previous = previous;
							}
						}
					}
				},
				id: nextId++,
				advice: advice,
				receiveArguments: receiveArguments
			};
		}
		if(previous && !around){
			if(type == "after"){
				// add the listener to the end of the list
				// note that we had to change this loop a little bit to workaround a bizarre IE10 JIT bug 
				while(previous.next && (previous = previous.next)){}
				previous.next = signal;
				signal.previous = previous;
			}else if(type == "before"){
				// add to beginning
				dispatcher[type] = signal;
				signal.next = previous;
				previous.previous = signal;
			}
		}else{
			// around or first one just replaces
			dispatcher[type] = signal;
		}
		return signal;
	}
	function aspect(type){
		return function(target, methodName, advice, receiveArguments){
			var existing = target[methodName], dispatcher;
			if(!existing || existing.target != target){
				// no dispatcher in place
				target[methodName] = dispatcher = function(){
					var executionId = nextId;
					// before advice
					var args = arguments;
					var before = dispatcher.before;
					while(before){
						if(before.advice){
							args = before.advice.apply(this, args) || args;
						}
						before = before.next;
					}
					// around advice
					if(dispatcher.around){
						var results = dispatcher.around.advice(this, args);
					}
					// after advice
					var after = dispatcher.after;
					while(after && after.id < executionId){
						if(after.receiveArguments){
							var newResults = after.advice.apply(this, args);
							// change the return value only if a new value was returned
							results = newResults === undefined ? results : newResults;
						}else{
							results = after.advice.call(this, results, args);
						}
						after = after.next;
					}
					return results;
				};
				if(existing){
					dispatcher.around = {advice: function(target, args){
						return existing.apply(target, args);
					}};
				}
				dispatcher.target = target;
			}
			var results = advise((dispatcher || existing), type, advice, receiveArguments);
			advice = null;
			return results;
		};
	}

	// TODOC: after/before/around return object

	var after = aspect("after");
	/*=====
	after = function(target, methodName, advice, receiveArguments){
		// summary:
		//		The "after" export of the aspect module is a function that can be used to attach
		//		"after" advice to a method. This function will be executed after the original method
		//		is executed. By default the function will be called with a single argument, the return
		//		value of the original method, or the the return value of the last executed advice (if a previous one exists).
		//		The fourth (optional) argument can be set to true to so the function receives the original
		//		arguments (from when the original method was called) rather than the return value.
		//		If there are multiple "after" advisors, they are executed in the order they were registered.
		// target: Object
		//		This is the target object
		// methodName: String
		//		This is the name of the method to attach to.
		// advice: Function
		//		This is function to be called after the original method
		// receiveArguments: Boolean?
		//		If this is set to true, the advice function receives the original arguments (from when the original mehtod
		//		was called) rather than the return value of the original/previous method.
		// returns:
		//		A signal object that can be used to cancel the advice. If remove() is called on this signal object, it will
		//		stop the advice function from being executed.
	};
	=====*/

	var before = aspect("before");
	/*=====
	before = function(target, methodName, advice){
		// summary:
		//		The "before" export of the aspect module is a function that can be used to attach
		//		"before" advice to a method. This function will be executed before the original method
		//		is executed. This function will be called with the arguments used to call the method.
		//		This function may optionally return an array as the new arguments to use to call
		//		the original method (or the previous, next-to-execute before advice, if one exists).
		//		If the before method doesn't return anything (returns undefined) the original arguments
		//		will be preserved.
		//		If there are multiple "before" advisors, they are executed in the reverse order they were registered.
		// target: Object
		//		This is the target object
		// methodName: String
		//		This is the name of the method to attach to.
		// advice: Function
		//		This is function to be called before the original method
	};
	=====*/

	var around = aspect("around");
	/*=====
	 around = function(target, methodName, advice){
		// summary:
		//		The "around" export of the aspect module is a function that can be used to attach
		//		"around" advice to a method. The advisor function is immediately executed when
		//		the around() is called, is passed a single argument that is a function that can be
		//		called to continue execution of the original method (or the next around advisor).
		//		The advisor function should return a function, and this function will be called whenever
		//		the method is called. It will be called with the arguments used to call the method.
		//		Whatever this function returns will be returned as the result of the method call (unless after advise changes it).
		// example:
		//		If there are multiple "around" advisors, the most recent one is executed first,
		//		which can then delegate to the next one and so on. For example:
		//		|	around(obj, "foo", function(originalFoo){
		//		|		return function(){
		//		|			var start = new Date().getTime();
		//		|			var results = originalFoo.apply(this, arguments); // call the original
		//		|			var end = new Date().getTime();
		//		|			console.log("foo execution took " + (end - start) + " ms");
		//		|			return results;
		//		|		};
		//		|	});
		// target: Object
		//		This is the target object
		// methodName: String
		//		This is the name of the method to attach to.
		// advice: Function
		//		This is function to be called around the original method
	};
	=====*/

	return {
		// summary:
		//		provides aspect oriented programming functionality, allowing for
		//		one to add before, around, or after advice on existing methods.
		// example:
		//	|	define(["dojo/aspect"], function(aspect){
		//	|		var signal = aspect.after(targetObject, "methodName", function(someArgument){
		//	|			this will be called when targetObject.methodName() is called, after the original function is called
		//	|		});
		//
		// example:
		//	The returned signal object can be used to cancel the advice.
		//	|	signal.remove(); // this will stop the advice from being executed anymore
		//	|	aspect.before(targetObject, "methodName", function(someArgument){
		//	|		// this will be called when targetObject.methodName() is called, before the original function is called
		//	|	 });

		before: before,
		around: around,
		after: after
	};
});