React-Router: how to wait for an async action before route transition

To answer the original question of preventing the transition to a new route until a response has succeeded or failed:

Because you're using redux thunk you could have the success or failure in the action creator trigger the redirect. I don't know what your specific action / action creator looks like but something like this could work:

import { browserHistory } from 'react-router'export function loadInitialFormValues(formId) {  return function(dispatch) {    // hit the API with some function and return a promise:    loadInitialValuesReturnPromise(formId)      .then(response => {        // If request is good update state with fetched data        dispatch({ type: UPDATE_FORM_STATE, payload: response });        // - redirect to the your form        browserHistory.push('/myForm');      })      .catch(() => {        // If request is bad...        // do whatever you want here, or redirect        browserHistory.push('/myForm')      });  }}

Follow up. Common pattern of loading data on entering a route / on componentWillMount of a component and displaying a spinner:

From the redux docs on async actions http://redux.js.org/docs/advanced/AsyncActions.html

• An action informing the reducers that the request began.

The reducers may handle this action by toggling an isFetching flag in the state. This way the UI knows it’s time to show a spinner.

• An action informing the reducers that the request finished successfully.

The reducers may handle this action by merging the new data into the state they manage and resetting isFetching. The UI would hide the spinner, and display the fetched data.

• An action informing the reducers that the request failed.

The reducers may handle this action by resetting isFetching. Additionally, some reducers may want to store the error message so the UI can display it.

I followed this general pattern below using your situation as a rough guideline. You do not have to use promises

// action creator:export function fetchFormData(formId) {  return dispatch => {    // an action to signal the beginning of your request    // this is what eventually triggers the displaying of the spinner    dispatch({ type: FETCH_FORM_DATA_REQUEST })    // (axios is just a promise based HTTP library)    axios.get(`/formdata/${formId}`)      .then(formData => {        // on successful fetch, update your state with the new form data        // you can also turn these into their own action creators and dispatch the invoked function instead        dispatch({ type: actions.FETCH_FORM_DATA_SUCCESS, payload: formData })      })      .catch(error => {        // on error, do whatever is best for your use case        dispatch({ type: actions.FETCH_FORM_DATA_ERROR, payload: error })      })  }}// reducerconst INITIAL_STATE = {  formData: {},  error: {},  fetching: false}export default function(state = INITIAL_STATE, action) {  switch(action.type) {    case FETCH_FORM_DATA_REQUEST:      // when dispatch the 'request' action, toggle fetching to true      return Object.assign({}, state, { fetching: true })    case FETCH_FORM_DATA_SUCCESS:      return Object.assign({}, state, {        fetching: false,        formData: action.payload      })    case FETCH_FORM_DATA_ERROR:      return Object.assign({}, state, {        fetching: false,        error: action.payload      })  }}// route can look something like this to access the formId in the URL if you want// I use this URL param in the component below but you can access this ID anyway you want:<Route path="/myForm/:formId" component={SomeForm} />// form componentclass SomeForm extends Component {  componentWillMount() {    // get formId from route params    const formId = this.props.params.formId    this.props.fetchFormData(formId)  }  // in render just check if the fetching process is happening to know when to display the spinner  // this could also be abstracted out into another method and run like so: {this.showFormOrSpinner.call(this)}  render() {    return (      <div className="some-form">        {this.props.fetching ?           <img src="./assets/spinner.gif" alt="loading spinner" /> :          <FormComponent formData={this.props.formData} />        }      </div>    )  }}function mapStateToProps(state) {  return {    fetching: state.form.fetching,    formData: state.form.formData,    error: state.form.error  }}export default connect(mapStateToProps, { fetchFormData })(SomeForm)

First and foremost, I want to say that there is a debate around the topic of fetching data with react-router's onEnter hooks whether or not is good practice, nevertheless this is how something like that would go:

You can pass the redux-store to your Router. Let the following be your Root component, where Router is mounted:

...import routes from 'routes-location';class Root extends React.Component {  render() {    const { store, history } = this.props;    return (      <Provider store={store}>        <Router history={history}>          { routes(store) }        </Router>      </Provider>    );  }}...

And your routes will be something like:

import ......const fetchData = (store) => {  return (nextState, transition, callback) => {    const { dispatch, getState } = store;    const { loaded } = getState().myCoolReduxStore;    // loaded is a key from my store that I put true when data has loaded    if (!loaded) {      // no data, dispatch action to get it      dispatch(getDataAction())        .then((data) => {          callback();        })        .catch((error) => {          // maybe it failed because of 403 forbitten, we can use tranition to redirect.          // what's in state will come as props to the component `/forbitten` will mount.          transition({            pathname: '/forbitten',            state: { error: error }          });          callback();        });    } else {      // we already have the data loaded, let router continue its transition to the route      callback();    }  }};export default (store) => {  return (    <Route path="/" component={App}>      <Route path="myPage" name="My Page" component={MyPage} onEnter={fetchData(store)} />      <Route path="forbitten" name="403" component={PageForbitten} />      <Route path="*" name="404" component={PageNotFound} />    </Route>  );};

Please notice that your router file is exporting a thunk with your store as argument, if you look upwards, see how we invoked the router, we pass the store object to it.

Sadly, at the time of writing react-router docs return 404 to me, thus I cannot point you to the docs where (nextState, transition, callback) are described. But, about those, from my memory:

• nextState describes the route react-router will transition to;

• transition function to preform maybe another transition than the one from nextState;

• callback will trigger your route transition to finish.

Another think to point out is that with redux-thunk, your dispatch action can return a promise, check it in the docs here. You can find here a good example on how to configure your redux store with redux-thunk.

I made a handy hook for this purpose, works with react-router v5:

/* * Return truthy if you wish to block. Empty return or false will not block */export const useBlock = func => {    const { block, push, location } = useHistory()    const lastLocation = useRef()    const funcRef = useRef()    funcRef.current = func    useEffect(() => {        if (location === lastLocation.current || !funcRef.current)            return        lastLocation.current = location        const unblock = block((location, action) => {            const doBlock = async () => {                if (!(await funcRef.current(location, action))) {                    unblock()                    push(location)                }            }            doBlock()            return false        })    }, [location, block, push])}

Inside your component, use it like:

const MyComponent = () => {    useBlock(async location => await fetchShouldBlock(location))    return <span>Hello</span>}

Navigation will not occur until the async function returns; you can completely block the navigation by returning true.