A map that lazily creates promises so that you can refer to possibly not yet existing promises by their id.

promiseMap

var promiseMap = function() {
  var api = {_: {}};

  api._.map = {};

  api._.getPromiseHandle = function(id) {
    var promiseHandle = api._.map[id];

    if (!promiseHandle) {
      promiseHandle = {
        set: false,
        deferred: RSVP.defer()
      };

      api._.map[id] = promiseHandle;
    }

    return promiseHandle;
  };

  api.resolve = function(id, value) {
    var promiseHandle = api._.getPromiseHandle(id);

    if (promiseHandle.set) {
      throw new Error('Promise ' + id + ' has already been set.');
    }

    promiseHandle.deferred.resolve(value);
    promiseHandle.set = true;
  };

  api.reject = function(id, value) {
    var promiseHandle = api._.getPromiseHandle(id);

    if (promiseHandle.set) {
      throw new Error('Promise ' + id + ' has already been set.');
    }

    promiseHandle.deferred.reject(value);
    promiseHandle.set = true;
  };

  api.get = function(id) {
    return api._.getPromiseHandle(id).deferred.promise;
  };
};