【avalon】createMap

/**
 * Creates a new object without a prototype. This object is useful for lookup without having to
 * guard against prototypically inherited properties via hasOwnProperty.
 *
 * Related micro-benchmarks:
 * - http://jsperf.com/object-create2
 * - http://jsperf.com/proto-map-lookup/2
 * - http://jsperf.com/for-in-vs-object-keys2
 */
function createMap() {
  return Object.create(null)
}