--harmony_modules (enable "harmony modules (implies block scoping)" (in progress))
  type: bool default: false
  --harmony_arrays (enable "harmony array methods" (in progress))
  type: bool default: false
  --harmony_array_includes (enable "harmony Array.prototype.includes" (in progress))
  type: bool default: false
  --harmony_regexps (enable "harmony regular expression extensions" (in progress))
  type: bool default: false
  --harmony_arrow_functions (enable "harmony arrow functions" (in progress))
  type: bool default: false
  --harmony_proxies (enable "harmony proxies" (in progress))
  type: bool default: false
  --harmony_sloppy (enable "harmony features in sloppy mode" (in progress))
  type: bool default: false
  --harmony_unicode (enable "harmony unicode escapes" (in progress))
  type: bool default: false
  --harmony_tostring (enable "harmony toString")
  type: bool default: false

但是看到 modules 和 arrow functions 还没有默认开启，感觉很伤心~~