React: useReducer hooks demo with nested select boxes

Today I got into a situation where I had to select the nested select box, that is, based on the value selected on the first select box, the values should be populated on the second select box.

This is the first time I’m trying hooks in react and wanted to experiment it. For this demo, I’m using react-select component.

The requirement is that the first select box will have list of countries. After I select one country, the second select box should be shown with the list of states of the selected country and the country select box should be disabled. Let’s build it!

Consider I’ve the data as follows:

const data = {
  countries: [
      value: 'INDIA',
      label: 'India',
      states: [
        { value: 'TAMIL NADU', label: 'Tamil Nadu' },
        { value: 'KERALA', label: 'Kerala' },
        { value: 'ANDHRA PRADESH', label: 'Andhra Pradesh' }
      value: 'US',
      label: 'USA',
      states: [
        { value: 'CA', label: 'California' },
        { value: 'NY', label: 'New York' }

And I’m setting up an initial state of my component:

const initialState = {
  disableCountry: false,
  disableState: true,
  loadingState: false,
  statesToBeLoaded: []

Then I create the reducer function with list of actions that I trigger from my component. The actions are when I select a country and when I click on a clear button to clear my selections:

const POPULATE_STATE = 'populateState'
const CLEAR = 'clear'
function reducer(state, action) {
  switch (action.type) {
      return {
        disableCountry: true,
        disableState: false,
        loadingState: true,
        statesToBeLoaded: data.countries.find(
          country => country.value ===
    case CLEAR:
      return initialState

Now I’m going to build my functional component which renders two select boxes:

function App() {
  const [state, dispatch] = useReducer(reducer, initialState)

  return (
    <div className="App">
      <h1>useReducer demo</h1>

        placeholder="Select Country..."
        onChange={e => dispatch({ type: POPULATE_STATE, country: e.value })}

      <br />

      {!state.disableState && (
            placeholder="Select State..."

          <br />

          <button type="button" onClick={() => dispatch({ type: CLEAR })}>

Here const [state, dispatch] = useReducer(reducer, initialState) I’m using useReducer function from the react which gives me back the current state and the dispatch method to trigger actions.

So I dispatch POPULATE_STATE during onChange event in my first select box to load the states of the selected country, and I dispatch CLEAR even when user clicked on Clear button to reset the state of the functional component.

This worked perfectly! We can extend this example to load the data from the external apis during our dispatch event and leverage loading state to display the progress indicator.

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