In CRA 5.0.0, `react-scripts start` fails when both `HOST` in `.env` and `proxy` in `package.json` are defined.

Describe the bug

In CRA 5.0.0, react-scripts start fails when both HOST in .env and proxy in package.json are defined.

Did you try recovering your dependencies?

This occurs on a newly created project.

Which terms did you search for in User Guide?

“allowedHosts” and others, came up empty.

Environment

Environment Info:

  current version of create-react-app: 5.0.0
  running from /home/z003w3we/.npm/_npx/c67e74de0542c87c/node_modules/create-react-app

  System:
    OS: Linux 5.4 Ubuntu 20.04.3 LTS (Focal Fossa)
    CPU: (4) x64 Intel(R) Core(TM) i7-9850H CPU @ 2.60GHz
  Binaries:
    Node: 16.13.0 - ~/.asdf/installs/nodejs/16.13.0/bin/node
    Yarn: 1.22.10 - ~/.asdf/shims/yarn
    npm: 8.1.3 - ~/.asdf/plugins/nodejs/shims/npm
  Browsers:
    Chrome: 96.0.4664.45
    Firefox: 95.0
  npmPackages:
    react: ^17.0.2 => 17.0.2 
    react-dom: ^17.0.2 => 17.0.2 
    react-scripts: 5.0.0 => 5.0.0 
  npmGlobalPackages:
    create-react-app: Not Found

Steps to reproduce

1. Create a new app.
2. Set HOST in .env.
3. Set proxy in package.json.
4. Run react-scripts start or something to that effect.

Expected behavior

App starts.

Actual behavior

I get this error:

> yarn start
yarn run v1.22.10
$ react-scripts start
Attempting to bind to HOST environment variable: test.localhost
If this was unintentional, check that you haven't mistakenly set it in your shell.
Learn more here: https://cra.link/advanced-config

Invalid options object. Dev Server has been initialized using an options object that does not match the API schema.
 - options.allowedHosts[0] should be a non-empty string.
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Reproducible demo

https://github.com/BalzGuenat/cra-test

[sunmoon-idegu]

The answer from josipat in

https://stackoverflow.com/questions/70374005/invalid-options-object-dev-server-has-been-initialized-using-an-options-object/70491173#70491173

works. I will just paste his answer here again, just for easy access.

1. Delete “proxy”: “http://localhost:xxxx” in package.json
2. run npm install http-proxy-middleware
3. Create a file setupProxy.js inside your src folder and write the following codes:

const { createProxyMiddleware } = require('http-proxy-middleware');

module.exports = function(app) {
  app.use(
    '/api',
    createProxyMiddleware({
      target: 'http://localhost:6000',
      changeOrigin: true,
    })
  );
};

1. run npm start

[hwinkler]

I encountered the problem when I tried:

HOST=<something>  yarn start

(and I have a proxy: setting in package.json).

I debugged a bit and found that in webpackDevServer.config.js#L46, allowedHosts is set to [undefined] because prepareUrls doesn’t set lanUrlForConfig if a host is specified.

By examining the code at that link I discovered the workaround:

HOST=<something>  DANGEROUSLY_DISABLE_HOST_CHECK=true  yarn start

Before you try that you should read the comment following webpackDevServer.config.js#L25 and determine whether that is dangerous for your situation. In my case it’s harmless.