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"（只是在 package.json 中更改），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. …