[eslint] Unexpected block statement surrounding arrow body; move the returned value immediately after the `=>`. [arrow-body-style]

[eslint] Unexpected block statement surrounding arrow body; move the returned value immediately after the `=>`. [arrow-body-style]

res => {

　　return new Promise().resolve(null);

}

本来是上面这样写，当只有一个返回的时候，eslint规定要写成：

res => (new Promise().resolve(null)); 

如果有多个返回，比如：

res => {

　　if (abc === true) {

　　　　return 0; // 第一个返回

      }

　　return 1; //  第二个返回

}

则不会报这个错，具体可以参照官方说明：

https://eslint.org/docs/rules/arrow-body-style