code: function clearCache() {
    let deletedCount = 0;
  
    const iter = eventSourceMappingKeysByFunctionAndStream.entries();
    let next = iter.next();
    while (!next.done) {
      const [k, key] = next.value;
  
      const deleted = eventSourceMappingPromisesByKey.delete(key);
      eventSourceMappingKeysByFunctionAndStream.delete(k);
  
      if (deleted) {
        ++deletedCount;
      }
  
      next = iter.next();
    }
  
    return deletedCount;
  }
docs: Clears the event source mapping key and promise caches.
  @return {number} the number of promises removed from the cache