我可以使用默认端口 3000 启动 React js。但是，当我将端口自定义为 4200 时，"start": "PORT=4200 react-scripts start"(刚刚在package.json)，我无法启动 React js 应用程序。

'PORT' is not recognized as an internal or external command,
operable program or batch file.
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! todo-app@0.1.0 start: `PORT=4200 react-scripts start`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the todo-app@0.1.0 start script.
npm ERR! This is probably not a problem with npm. There is likely additional lo
ging output above.

npm ERR! A complete log of this run can be found in: