Comparison between (my) old callback-structured code, @getify's asynquence refactor, and my async refactor

async.js

var doQuery = function() {
	
	// passing an object to async.parallel will cause it to collect their results
	// and provide them to the callback in an object with the same keys.
	
	async.parallel({
		// functions are passed a callback with the standard argument pattern of fn(err, result)
		count: count.exec,
		query: query.exec
	}, function(err, results) {
		
		// if either method returns a truthy err argument, the main callback is
		// executed immediately and passed the error. send it on and exit.
		if (err) return sendError('database error', err);
		
		// transform the data and send it via `sendResponse()`
		sendResponse({
			total: results.count,
			items: results.query.map(function(i) {
				return {
					name: req.list.getDocumentName(i, true) || '(' + i.id + ')',
					id: i.id
				};
			})
		});
		
	});
	
}

asynquence.js

var doQuery = function() {
	// fetch total
	return ASQ(function(done){
		count.exec(function(err, total) {
			// note: `return` here does nothing for asynquence, only
			// exits the function early. :)
			if (err) return done.fail('database error', err);
			
			done(total); // pass along `total` as a value-message
		});
	})
	// fetch items
	.then(function(done, total){
		query.exec(function(err, items) {
			// note: `return` here does nothing for asynquence, only
			// exits the function early. :)
			if (err) return done.fail('database error', err);
	
			done(total,items); // pass along both as value-messages
		})
	})
	// transform the data to prepare it for `sendResponse()`
	.val(function(total, items){
		return {
			total: total,
			items: items.map(function(i) {
				return {
					name: req.list.getDocumentName(i, true) || '(' + i.id + ')',
					id: i.id
				};
			})
		};
	})
	// now, send the transformed data along
	.val(sendResponse)
	// handle any errors that propagate up to here
	.or(sendError);
}

old.js

var doQuery = function() {
	count.exec(function(err, total) {
		
		if (err) return sendError('database error', err);
		
		query.exec(function(err, items) {
			
			if (err) return sendError('database error', err);
			
			sendResponse({
				total: total,
				items: items.map(function(i) {
					return {
						name: req.list.getDocumentName(i, true) || '(' + i.id + ')',
						id: i.id
					};
				})
			});
			
		});
		
	});
}