What is withRouter for in react-router-dom?

When you include a main page component in your app, it is often wrapped in a <Route> component like this:

<Route path="/movies" component={MoviesIndex} />

By doing this, the MoviesIndex component has access to this.props.history so it can redirect the user with this.props.history.push.

Some components (commonly a header component) appear on every page, so are not wrapped in a <Route>:

render() {
  return (<Header />);
}

This means the header cannot redirect the user.

To get around this problem, the header component can be wrapped in a withRouter function, either when it is exported:

export default withRouter(Header)

This gives the Header component access to this.props.history, which means the header can now redirect the user.