方案一：配置proxy

1. 弹射出react详细配置 yarn eject
2. 修改config\webpackDevServer.config.js

    proxy: {
      "/api": {
        target: "http://localhost:3000",
        changeOrigin: true,
        // pathRewrite: {
        //   "^/api": ""
        // }
      }
    },

方案二：http-proxy-middleware

1. yarn add http-proxy-middleware -S
2. src目录下新建文件setupProxy.js

const { createProxyMiddleware } = require("http-proxy-middleware");
module.exports = function (app) {
  app.use(
    createProxyMiddleware("/api", {
      target: "http://localhost:3000",
      changeOrigin: true,
      // pathRewrite: {
      //   "^/api": ""
      // }
    })
  )
}

React create-react-app跨域解决方案