CreateCallback.js, a callback creator/manager for client or server-side

CreateCallback.js

var CreateCallback = (function() {
	var pool = [];
	
	function CreateCallback() {
		if(pool.length){
			var callback = pool.pop();
		}
		else {
			function callback() {
				if(callback.action){
					Array.prototype.push.call(arguments, callback);
					callback.action.apply(this, arguments);
				}
			}
			callback.action = null;
			callback.dispose = _dispose.bind(callback);
			callback.dispose.disposed = false;
			callback.setAction = _setAction;
		}
		
		return callback;
	}
	CreateCallback.pool = pool;
	CreateCallback.maxPoolSize = Infinity;
	
	function _setAction(action){
		this.action = action;
		return this;
	}
	function _dispose(){
		if (!this.dispose.disposed) {
			if (pool.length < CreateCallback.maxPoolSize) {
				pool.push(this);
			}
			this.action = null;
 
			if (this.onDispose) { this.onDispose(this); }
 
			this.dispose.disposed = true;
		}
		
		return this;		
	}
	
	return CreateCallback;
})();
 
if (undefined !== module) { module.exports = CreateCallback; }

demo.js

CreateCallback.maxPoolSize = 10; // pooled callbacks will never exceed this number (defaults to Infinity)
 
var callback = CreateCallback(); // creates a new callback function, or takes one from the pool if available
// setup
callback.var1 = 1;
callback.filepath = filepath;
callback.request = request;
callback.response = response;
// callback.action = action; // does the same thing as setAction
 
callback.onDispose = function() { // called after disposal and pooling
	// cleanup
	delete callback.var1;
	delete callback.request;
	delete callback.response;
};
 
// setAction(action) == action will be called with added 'callback' argument after existing arguments
fs.exists(filepath, callback.setAction(exists));
 
function exists(exists, callback) {
	// 'exists' comes from the fs.exists callback trigger; any existing arguments are kept intact
	// 'callback' is the original callback function, to be read from, reused, or disposed of
	
	callback.var1 // == 1; properties set in setup persist
	response.write("hello world!"); // including objects
	response.end();
	
	if (!exists) {
		callback.response.write("404")
		callback.response.end();
		
		// .dispose() resets and pools the callback if applicable
		// this is not required, but will help protect against Garbage Collection
		callback.dispose();
	
		CreateCallback.pool.length // == 1
	}
	else {
		// callback.dispose can be used directly as an event listener
		fs.createReadStream(callback.filepath).on("end", callback.dispose).pipe(response);
	}
}