0-cache-args.js

0-cache-args.js

// our own in memory database
var users = {
  'alex': { user: 'alex', age: 27 },
  'john': { user: 'johndoe', age: 34 }
};

// async function
var getUserFromDb = function getUserFromDb(id, callback) {
  var min = 1000;
  var max = 2000;
  var randomTimeout = Math.floor(Math.random() * (max - min + 1)) + min;

  setTimeout(function() {
    callback(null, users[id] || null);
  }, randomTimeout);
};

var cachify = function cachify(originalFn, getFromCache) {
  return function() {
    var args = Array.prototype.slice.call(arguments);
    // get callback and remove it from the `args` array
    var originalCb = args.pop();
    var that = this;

    // put a custom callback instead, so we know to call the original function
    // on cache miss
    args.push(function(err, result) {
      if (err) { return originalCb(err); }

      if (typeof result === 'undefined' || result === null) {
        // cache miss

        // put the original callback where it belongs, as the last argument
        args[args.length - 1] = originalCb;
        // args.push(originalCb);

        originalFn.apply(that, args);
      } else {
        // cache hit
        originalCb(null, result);
      }
    });

    getFromCache.apply(this, args);
  };
};

var getResultFromCache = function getResultFromCache(id, cb) {
  setTimeout(function() {
    cb(null, users[id] || null);
  }, 0);
};

// Example:
// this takes between 1-2 seconds to get the result
console.time('database');
getUserFromDb('alex', function(err, user) {
  if (err) { throw err; }

  console.log('directly hitting the database:', user);
  console.timeEnd('database');
});

// this should be much faster
console.time('cache');
var cachedAsyncFunction = cachify(getUserFromDb, getResultFromCache);
cachedAsyncFunction('alex', function(err, result) {
  if (err) { throw err; }

  console.log('from cache:', result);
  console.timeEnd('cache');
});