robojones/better-events

/**
 * Cache eventPromises
 * @param {Object} cache - The cache object.
 * @param {string} eventName - The name of the event.
 * @param {function} fn - The inner function for the promise.
 */
function eventPromiseCache(source, cacheProp, eventName, fn) {
  if (!source[cacheProp]) {
    source[cacheProp] = {}
  }

  const cache = source[cacheProp]
  if (!cache[eventName]) {
    cache[eventName] = new Promise((resolve, reject) => {
      function deleteAnd(fn) {
        // delete wrapper
        return result => {
          delete cache[eventName]
          fn(result)
        }
      }

      fn(deleteAnd(resolve), deleteAnd(reject))
    })
  }

  return cache[eventName]
}

module.exports = eventPromiseCache