为什么巴贝尔要把异步函数变成节点8.10的生成器?

如果node 8.10支持async/await,那么babel为什么要将异步函数转换为生成器呢?

巴贝尔翻译:

const foo = async () => {
  const b = await bar()
  console.log(b)
}

分为:

const foo = (() => {
  var _ref2 = (0, _asyncToGenerator3.default)(function* () {
    const b = yield bar();
    console.log(b);
  });

  return function foo() {
    return _ref2.apply(this, arguments);
  };
})()

这是我的babel配置:

  "babel": {
    "plugins": [
      "source-map-support",
      "transform-runtime"
    ],
    "presets": [
      [
        "env",
        {
          "targets": {
            "node": "8.10"
          }
        }
      ],
      "stage-3"
    ]
  }