Is it possible to match the # part of a route in React Router 4

if you actually want to match and get the parameters, use matchPath.

import { useLocation, matchPath } from 'react-router-dom';

// your route you want to see if it matches
const routePath = '/overtherainbow/:country/#/city/:city/detail'

// somewhere while rendering
const location = useLocation();
useEffect(() => {
  const matched = matchPath(location.pathname + location.hash, routePath);
  if (matched){
    // matched, do something with it, like setting state, fetching data or what not
    console.log(matched.params); // will be {country:..., city:...}
  }
}, [location])

@azium answer works fine as long as you don't need to use render or children prop in HashRoute. In which case this solution will work better :

import React from 'react';
import { Route } from 'react-router-dom';

const HashRoute = ({ hash, ...routeProps }) => (
  <Route
    render={({ location }) => (
      (location.hash === hash) && <Route {...routeProps} />
    )}
  />
);

export default HashRoute;

Use it like that :

<HashRoute hash="#modalB" component={ModalB} />

Or combine it with route matching :

<HashRoute hash="#modalB" path="/subPageOnly" component={ModalB} />

Not out of the box, but the beauty of React Router 4 is that it's incredibly easy to implement this yourself.

let HashRoute = ({ component: Component, path, ...routeProps }) => (
  <Route 
    {...routeProps}
    component={({ location, ...props }) =>
      location.hash === path && <Component {...props} />
    }
  />
)

<HashRoute path="#modalB" component={ModalB} />