How can I serve robots.txt on an SPA using React with Firebase hosting?

In my /public directory, I created a robots.txt.

In my /src directory, I did the following:

I created /src/index.js:

import React from 'react'
import ReactDOM from 'react-dom'
import {TopApp} from './TopApp'
import registerServiceWorker from './registerServiceWorker'

import {BrowserRouter} from 'react-router-dom'

ReactDOM.render(
  <BrowserRouter>
    <TopApp/>
  </BrowserRouter>,
  document.getElementById('react-render-root')
)

registerServiceWorker()

I created /src/TopApp.js:

import React from 'react'

import {
  Switch,
  Route
} from 'react-router-dom'

import {ComingSoon} from './ComingSoon'
import {App} from './App'

export class TopApp extends React.Component {
  render() {
    return (
      <div className="TopApp">
        <Switch>
          <Route path='/MyStuff' component={App}/>
          <Route exact path='/' component={ComingSoon}/>
        </Switch>
      </div>
    )
  }
}

Because path /robots.txt is not covered by the router paths provided, it took it from my public directory and robots file was published as desired.

The same could be done for sitemap.xml.

Just add the following rules to the "rewrites" section in firebase.json

"rewrites": [
      {
        "source": "/robots.txt",
        "destination": "/robots.txt"
      },
      {
        "source": "**",
        "destination": "/index.html"
      }
]