forgetful.js

/*
  testing a forgetful memoized promise: A promise, memoized which is forgotten after a given duration.
*/ 
var Q = require('q');
var _ = require('underscore');

function expensive( req ){
  var result = Q.defer();
  var msg = JSON.stringify(req);
  console.log(new Date() + ' about to do something expensive: ' + msg);
  setTimeout(function(){
	  console.log('expensive op complete: ' + msg);
    result.resolve('boo ' + msg);
	}, 4200);
  return result.promise;
}
function log( result ){
  console.log(new Date() + ' ' + result);
}
function hasher(req){
  return req.id;
}
function forget(expensive, lapsed, hasher){
  var memoized = _.memoize(expensive, hasher);
  if (!memoized.forgetting){
	  memoized.forgetting = {};
  }
  return function(){
	  var result = memoized.apply(null,arguments); // warning null
	  var hash = hasher.apply(null,arguments);     // warning null
	  if (!memoized.forgetting[hash]){
	    memoized.forgetting[hash] = true;
	    setTimeout(function(){
			  delete memoized.cache[hash];
			  delete memoized.forgetting[hash];
	    },lapsed);
	  }
	  return result;
  };
}
var forgetful = forget(expensive, 12000, hasher);
var t = 30;
function loop(){
  if (t > 0){
	  forgetful({id: t % 3 }).then(log);
	  setTimeout(loop, 1000);
	  t--;
  }
}
loop();
module.exports = forget;