I've tried everything suggested here but didn't work for me. So in case I can help anyone with a similar issue, every single tutorial I've checked is not updated to work with version 4.
Here is what I've done to make it work
import React from 'react';
import App from './App';
import ReactDOM from 'react-dom';
import {
HashRouter,
Route
} from 'react-router-dom';
ReactDOM.render((
<HashRouter>
<div>
<Route path="/" render={()=><App items={temasArray}/>}/>
</div>
</HashRouter >
), document.getElementById('root'));
That's the only way I have managed to make it work without any errors or warnings.
In case you want to pass props to your component for me the easiest way is this one:
<Route path="/" render={()=><App items={temasArray}/>}/>