Memoize requests

memoize_server.js

var http = require('http'), EventEmitter = require('events').EventEmitter;
var cache = {};

http.createServer(function (req, res) {
   var key = someMagic(req), cached = cache[key]; // get some unique request identifier

   if (!cached) { // if we've never seen this request before
     cached = new EventEmitter(); // make this cache entry an event emitter
     cached.status = 'running';
     handleAsyncRequest(function(result) { // your request handling is probably asynchronous, call this callback when you're done
       cached.response = result; // memoize data
       cached.status = 'finished';
       cached.emit('finished'); // notify all observers waiting for this request
     });

   } else {
     switch(cached.status) { // if existing request, check if it's still running or finished
       case 'finished':
         res.end(cached.response); // send cached response immediately if request has finished
         break;
       case 'running':
         // subscribe as observer; send response when request is finished
         cached.once('finished', function() { res.end(cached.response); });
         break;
     }
   }
}).listen(1337, "127.0.0.1");