`memoizeUntil` -- memoize function for n milliseconds

memoize-until.js

var R = require("ramda");

var memoizeUntil = function (fn, expiry) {

    var cache = {};
    var onExpiry = [];
    var onCache = [];
    var onCachedResult = [];

    var memoized = function () {
        var args = Array.prototype.slice.call(arguments, 0);
        var hash = hashArgs(args);
        var result;
        if (!R.has(hash, cache)) {
            result = fn.apply(this, args);
            cache[hash] = result;
            R.forEach(function(f) { f(result, args, expiry); }, onCache);
            setTimeout(function() {
                var v = cache[hash];
                delete cache[hash];
                R.forEach(function(f) { f(v, args, expiry); }, onExpiry);
            }, expiry);
        } else {
            result = cache[hash];
            R.forEach(function(f) { f(result, args, expiry); }, onCachedResult);
        }
        return result;
    };

    memoized.onExpiry = function (f) {
      onExpiry = R.concat(onExpiry, [f]);
      return memoized;
    };

    memoized.onCache = function (f) {
        onCache = R.concat(onCache, [f]);
        return memoized;
    };

    memoized.onCachedResult = function (f) {
        onCachedResult = R.concat(onCachedResult, [f]);
    };

    return memoized;
};

var getAuthToken = function () {
  return new Promise(...);
};

getAuthToken = memoizeUntil(getAuthToken, 10 * 60 * 1000); // Remember until 10 minutes has passed.

getAuthToken.onCache(function (token, args, timeout) {
  console.log("Caching auth token for appId `" + args[0] + "` for " + (timeout / 1000) + " seconds");
});

getAuthToken.onCachedResult(function(token, args, expiry) {
  token.then(function (token) {
    console.log("Returning cached token: `" + token + "`");
  });
});

getAuthToken.onExpiry(function(token, args, expiry) {
  console.log(String(expiry / 1000) + " seconds has elapsed -- cached token for appId `" + args[0] + "` has expired.");
});


getAuthToken(appId, appSecret).then(function() { ... }); // -> "Caching auth token for appId `myaddid` for 600 seconds
getAuthToken(appId, appSecret).then(function() { ... }); // -> "Returning cached token: `...`
getAuthToken(appId, appSecret).then(function() { ... }); // -> "Returning cached token: `...`
getAuthToken(appId, appSecret).then(function() { ... }); // -> "Returning cached token: `...`

setTimeout(function() {
  getAuthToken(appId, appSecret).then(function() { ... }); // -> "Returning cached token: `...`
}, 5 * 60 * 1000); // Wait 5 minutes.

setTimeout(function() {
  console.log("Token should have expired by now...");
  getAuthToken(appId, appSecret).then(function() { ... }); 
}, 11 * 60 * 1000); // Wait 11 minutes.

//10 minutes after...
// console.log -> 600 seconds has elapsed -- cached token for appId `myaddid` has expired.

//11 minutes after...
// console.log -> Token should have expired by now...
// console.log -> "Returning cached token: `...`