环境变量.env文件修改
# 自定义 react-scripts 服务端口 ，默认3000
PORT = 8000
源码位置 https://github.com/facebook/create-react-app/blob/main/packages/react-scripts/scripts/start.js
// Tools like Cloud9 rely on this.
const DEFAULT_PORT = parseInt(process.env.PORT, 10) || 3000;
const HOST = process.env.HOST || '0.0.0.0';
