Comment by gobengo

  $> diff <(node --v8-options | grep harmony) <(./iojs --v8-options | grep harmony)
  1,6c1,18
  <   --harmony_typeof (enable harmony semantics for typeof)
  <   --harmony_scoping (enable harmony block scoping)
  <   --harmony_modules (enable harmony modules (implies block scoping))
  <   --harmony_proxies (enable harmony proxies)
  <   --harmony_collections (enable harmony collections (sets, maps, and weak maps))
  <   --harmony (enable all harmony features (except typeof))
  ---
  >   --es_staging (enable all completed harmony features)
  >   --harmony (enable all completed harmony features)
  >   --harmony_shipping (enable all shipped harmony fetaures)
  >   --harmony_modules (enable "harmony modules (implies block scoping)" (in progress))
  >   --harmony_arrays (enable "harmony array methods" (in progress))
  >   --harmony_array_includes (enable "harmony Array.prototype.includes" (in progress))
  >   --harmony_regexps (enable "harmony regular expression extensions" (in progress))
  >   --harmony_arrow_functions (enable "harmony arrow functions" (in progress))
  >   --harmony_proxies (enable "harmony proxies" (in progress))
  >   --harmony_sloppy (enable "harmony features in sloppy mode" (in progress))
  >   --harmony_unicode (enable "harmony unicode escapes" (in progress))
  >   --harmony_tostring (enable "harmony toString")
  >   --harmony_numeric_literals (enable "harmony numeric literals")
  >   --harmony_strings (enable "harmony string methods")
  >   --harmony_scoping (enable "harmony block scoping")
  >   --harmony_classes (enable "harmony classes (implies block scoping & object literal extension)")
  >   --harmony_object_literals (enable "harmony object literal extensions")
  >   --harmony_templates (enable "harmony template literals")