Index: frontend/node_modules/tryer/src/tryer.js
===================================================================
--- frontend/node_modules/tryer/src/tryer.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
+++ frontend/node_modules/tryer/src/tryer.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
@@ -0,0 +1,210 @@
+// Conditional and repeated task invocation for node and browser.
+
+/*globals setTimeout, define, module */
+
+(function (globals) {
+  'use strict';
+
+  if (typeof define === 'function' && define.amd) {
+    define(function () {
+      return tryer;
+    });
+  } else if (typeof module !== 'undefined' && module !== null) {
+    module.exports = tryer;
+  } else {
+    globals.tryer = tryer;
+  }
+
+  // Public function `tryer`.
+  //
+  // Performs some action when pre-requisite conditions are met and/or until
+  // post-requisite conditions are satisfied.
+  //
+  // @option action {function} The function that you want to invoke. Defaults to `() => {}`.
+  //                           If `action` returns a promise, iterations will not end until
+  //                           the promise is resolved or rejected. Alternatively, `action`
+  //                           may take a callback argument, `done`, to signal that it is
+  //                           asynchronous. In that case, you are responsible for calling
+  //                           `done` when the action is finished.
+  //
+  // @option when {function}   Predicate used to test pre-conditions. Should return `false`
+  //                           to postpone `action` or `true` to perform it. Defaults to
+  //                           `() => true`.
+  //
+  // @option until {function}  Predicate used to test post-conditions. Should return `false`
+  //                           to retry `action` or `true` to terminate it. Defaults to
+  //                           `() => true`.
+  //
+  // @option fail {function}   Callback to be invoked if `limit` tries are reached. Defaults
+  //                           to `() => {}`.
+  //
+  // @option pass {function}   Callback to be invoked after `until` has returned truthily.
+  //                           Defaults to `() => {}`.
+  //
+  // @option interval {number} Retry interval in milliseconds. A negative number indicates
+  //                           that subsequent retries should wait for double the interval
+  //                           from the preceding iteration (exponential backoff). Defaults
+  //                           to -1000.
+  //
+  // @option limit {number}    Maximum retry count, at which point the call fails and retries
+  //                           will cease. A negative number indicates that retries should
+  //                           continue indefinitely. Defaults to -1.
+  //
+  // @example
+  //   tryer({
+  //     when: () => db.isConnected,
+  //     action: () => db.insert(user),
+  //     fail () {
+  //       log.error('No database connection, terminating.');
+  //       process.exit(1);
+  //     },
+  //     interval: 1000,
+  //     limit: 10
+  //   });
+  //
+  // @example
+  //   let sent = false;
+  //   tryer({
+  //     until: () => sent,
+  //     action: done => {
+  //       smtp.send(email, error => {
+  //         if (! error) {
+  //           sent = true;
+  //         }
+  //         done();
+  //       });
+  //     },
+  //     pass: next,
+  //     interval: -1000,
+  //     limit: -1
+  //   });
+  function tryer (options) {
+    options = normaliseOptions(options);
+
+    iterateWhen();
+
+    function iterateWhen () {
+      if (preRecur()) {
+        iterateUntil();
+      }
+    }
+
+    function preRecur () {
+      return conditionallyRecur('when', iterateWhen);
+    }
+
+    function conditionallyRecur (predicateKey, iterate) {
+      if (! options[predicateKey]()) {
+        incrementCount(options);
+
+        if (shouldFail(options)) {
+          options.fail();
+        }  else {
+          recur(iterate, postIncrementInterval(options));
+        }
+
+        return false;
+      }
+
+      return true;
+    }
+
+    function iterateUntil () {
+      var result;
+
+      if (isActionSynchronous(options)) {
+        result = options.action();
+
+        if (result && isFunction(result.then)) {
+          return result.then(postRecur, postRecur);
+        }
+
+        return postRecur();
+      }
+
+      options.action(postRecur);
+    }
+
+    function postRecur () {
+      if (conditionallyRecur('until', iterateUntil)) {
+        options.pass();
+      }
+    }
+  }
+
+  function normaliseOptions (options) {
+    options = options || {};
+    return {
+      count: 0,
+      when: normalisePredicate(options.when),
+      until: normalisePredicate(options.until),
+      action: normaliseFunction(options.action),
+      fail: normaliseFunction(options.fail),
+      pass: normaliseFunction(options.pass),
+      interval: normaliseNumber(options.interval, -1000),
+      limit: normaliseNumber(options.limit, -1)
+    };
+  }
+
+  function normalisePredicate (fn) {
+    return normalise(fn, isFunction, yes);
+  }
+
+  function isFunction (fn) {
+    return typeof fn === 'function';
+  }
+
+  function yes () {
+    return true;
+  }
+
+  function normaliseFunction (fn) {
+    return normalise(fn, isFunction, nop);
+  }
+
+  function nop () {
+  }
+
+  function normalise (thing, predicate, defaultValue) {
+    if (predicate(thing)) {
+      return thing;
+    }
+
+    return defaultValue;
+  }
+
+  function normaliseNumber (number, defaultNumber) {
+    return normalise(number, isNumber, defaultNumber);
+  }
+
+  function isNumber (number) {
+    return typeof number === 'number' && number === number;
+  }
+
+  function isActionSynchronous (options) {
+    return options.action.length === 0;
+  }
+
+  function incrementCount (options) {
+    options.count += 1;
+  }
+
+  function shouldFail (options) {
+    return options.limit >= 0 && options.count >= options.limit;
+  }
+
+  function postIncrementInterval (options) {
+    var currentInterval = options.interval;
+
+    if (options.interval < 0) {
+      options.interval *= 2;
+    }
+
+    return currentInterval;
+  }
+
+  function recur (fn, interval) {
+    setTimeout(fn, Math.abs(interval));
+  }
+}(this));
+