code: function DB() {
    this.requests = {}
    process.on('message', function(message) {
      if (message.type !== 'cache:response') {
        return
      }
  
      /** @type {{error: Error, response: string, uid: string, method: string}} */
      var data = message.data
      // The requests for this UID may not exist because there can be multiple
      // instances of Impromptu.
      if (!(this.requests[data.method] && this.requests[data.method][data.uid])) {
        return
      }
  
      var callbacks = this.requests[data.method][data.uid]
      for (var i = 0; i < callbacks.length; i++) {
        var callback = callbacks[i]
        callback(data.error, data.response)
      }
  
      delete this.requests[data.method][data.uid]
    }.bind(this))
  }
docs: The Impromptu database client.
  @constructor