resolve parameters in expressjs

api.js

var server = require('./server.js');
var collection = require('./collection.js');

var app = server();

app.put('/items/:id/part', server.resolve(collection), function(req, res){
		
		// no more 404 checking
		
		// access resolved item
		var item = req.resolved;
    item.part = req.body;
  
    // ...
});

server.js

var express = require('express');

express.resolve = function(collection, param){
	return function(req, res, next){
		collection.get(req.params[param || 'id']).then(function (item) {
			if(!item) {
				res.send(404);
				return;
			}

			req.resolved = item;
			next();
		});
	};
};