voice tech

Handling Speech Input in a React App

Ari Nykänen

Dec 18, 2020

7 min read

Learn the best practices for handling speech input in a Speechly React app.

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To demonstrate writing voice-enabled apps in practice, we’ll build a smart home controller app that responds with real-time visual feedback to spoken commands like:

"Switch off the radio in the living room."

"Turn on the lights in the bedroom."

Design goals

The app is going to be built on two design pillars in particular:

  • Responsiveness, so that the user is confident that the app follows the user’s speech.

  • Robustness, so that app behaves nicely even if the interpretation of the user’s intents changes during the sentence.

Understanding real-time speech recognition

By definition, speech-to-text systems give you text (transcript) to work with. Real-time systems provide partial sentences as soon as words are recognised and continue to refine the transcript as the speech progresses.

In addition to this, Speechly, for one, goes a step further by providing you with tagged keywords (entities) and the intent of the sentence as soon as they are recognised. At first, they would be tagged as tentative, and later turn to final.

The above example sentences would be deconstructed as follows:

"Switch off the radio in the living room"

_→ _Intent: turn_off, entities: radio (of type device), living room (of type room)

The tags are defined in a voice interface configuration in Speechly Annotation Language (SAL). While I’ve pre-configured the keywords for this example, you can learn how to create your own voice interfaces here.

While we're getting a constant stream of words as the sentence is being uttered, the speaker’s true intentions are only confirmed at the end of sentence (which Speechly calls a final segment).


Let’s assume the user would say "Turn the kitchen lights... on".

If we would wait until the end of the sentence before providing any feedback to the user, the time from manipulation (speech) to desired effect may increase to several seconds, rendering the user experience unresponsive and clumsy.

To mitigate this, we will highlight the objects mentioned in the sentence (appliances like "lights" and rooms) to give the user an early confirmation of where and what changes would happen. The speaker may even use this near real-time information to alter his spoken command.

If we wanted, we could even take a more forward leaning approach by actually toggling the lights when we have enough information about the user's intent.


To deliver the robust experience users expect, we need to be prepared for the (luckily, rare) occasion that the intent changes as the speech progresses, sometimes at the very last moment. What if the user would have finished the above sentence with an ""?

We'll facilitate the changes (big or small) by storing a copy of the app state when the user starts a new sentence. Then we simply recalculate the new state over and over again using the information we receive as the user speaks. By operating on the whole app state allows speech to control all aspects of the application: adding, removing and modifying data on any number of objects are all handled in a similar manner. Reflecting the information upon the last stable state becomes especially important should the interpretation of the user’s intent change in the middle of the sentence. Finally we store the last tentative state as the new stable state for upcoming sentences.

This approach assumes that your app state is fairly compact so that you can effectively create a new copy of the entire app state upon new information becomes available from the speech to text engine, which may occur up to 10 times a second. Also, the user interface needs to be fast enough to keep up with state updates so that won't choke the performance.

Demonstrating the key concepts in a home automation app

Let's create a sample app to see how it all comes together.

I'm assuming that you have some experience with React so you probably already have node/npm installed. If you want run the demo, prepare a React TypeScript project, but with contents of src/App.tsx replaced with this Gist like so:

npx create-react-app home-automation --template typescript
cd home-automation
# Download and replace src/App.tsx with the Home Automation app
curl > src/App.tsx
# Install dependencies
npm install
npm install @speechly/react-client @speechly/react-ui
npm start

Before walking thru the code, a word about some of the choices I’ve made:

  • I used TypeScript with React to help me avoid the dumbest mistakes with the code. More info about TypeScript in React here.
  • I'm using a home automation voice interface defined in Speechly’s SAL syntax and pre-deployed so we can just use it in the following code. More about that here.
  • Some implicit styling is visible in some of the snippets. A reminder from my StyledComponents experiments, but without the dependency...

Rendering the app

The main render function is probably pretty much what you’d expect it to be in a React app. The whole of the app is wrapped in a <SpeechProvider> which connects to the Speechly cloud services and enables speech-to-text for any contained component. The appId points to a pre-configured voice interface that defines the keywords and phrases you can use in this app.

export default function App() {
  return (
    <div className="App">
          <BigTranscript />
        <SpeechlyApp />
          <PushToTalkButton captureKey=" " />

Data model for the app state

The app has a monolithic state object (think of a React/Redux store). The data model is just a collection of rooms with device states in them. It’s worth noting that the names match those of the entities defined in the voice interface configuration mentioned above. This way the entities returned by the speech-to-text API are easy to connect with the model.

const DefaultAppState = {
  rooms: {
    'living room': {
      radio: false,
      television: false,
      lights: false,
    bedroom: {
      radio: false,
      lights: false,
    kitchen: {
      radio: false,
      lights: false,

Interpreting the speech segment

The details of the state manipulation logic reside in alterAppState, which takes the segment and last “stable” appstate and returns a new app state object with segment information reflected on it.

selectedRoom and selectedDevice are used to highlight the objects the user talks in the user interface.

const alterAppState = useCallback(
  (segment: SpeechSegment): AppState => {
    switch (segment.intent.intent) {
      case 'turn_on':
      case 'turn_off':
        // Get values for room and device entities.
        const room = segment.entities
          .find((entity) => entity.type === 'room')
        const device = segment.entities
          .find((entity) => entity.type === 'device')
        // Set desired device powerOn based on the intent
        const isPowerOn = segment.intent.intent === 'turn_on';
        if (
          room &&
          device &&
          appState.rooms[room] !== undefined &&
          appState.rooms[room][device] !== undefined
        ) {
          return {
            rooms: {
              [room]: { ...appState.rooms[room], [device]: isPowerOn },
    return appState;

The stable and the tentative app state

As the user speaks, the useEffect below fires as a response to changed words, entities and intent in segment. The new tentativeAppState is then resolved by calling alterAppState. Upon the end of the sentence (indicated by the segment.isFinal flag) the last tentativeAppState is stored as the new “stable” appState.

function SpeechlyApp() {
  const { segment } = useSpeechContext();
  const [tentativeAppState, setTentativeAppState] = useState<AppState>(DefaultAppState);
  const [appState, setAppState] = useState<AppState>(DefaultAppState);
  const [selectedRoom, setSelectedRoom] = useState<string | undefined>();
  const [selectedDevice, setSelectedDevice] = useState<string | undefined>();

  // This effect is fired whenever there's a new speech segment available
  useEffect(() => {
    if (segment) {
      let alteredState = alterAppState(segment);
      // Set current app state
      if (segment.isFinal) {
        // Store the final app state as basis of next utterance
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [segment]);

Rendering the app state

The remaining part is rendering the rooms as boxes with devices in them. The renderer uses the information both in the appState and tentativeState to highlight changes to the device states. The selected room and devices are also visualised during the utterance.

return (
        display: "flex",
        height: "100vh",
        flexDirection: "row",
        justifyContent: "center",
        alignItems: "center",
        alignContent: "center",
        flexWrap: "wrap",
      {Object.keys(appState.rooms).map((room) => (
            width: "12rem",
            height: "12rem",
            padding: "0.5rem",
            borderWidth: "2px",
            borderStyle: "solid",
            borderColor: selectedRoom === room ? "cyan" : "black",
              paddingTop: "1rem",
              display: "flex",
              flexDirection: "row",
              justifyContent: "start",
              alignItems: "start",
              flexWrap: "wrap",
            {Object.keys(appState.rooms[room]).map((device) => (
                  flexBasis: "5rem",
                  margin: "0.2rem",
                  padding: "0.2rem",
                    selectedDevice === device &&
                    (!selectedRoom || selectedRoom === room)
                      ? "cyan"
                      : "lightgray",
                <br />
                {appState.rooms[room][device] ? (
                  tentativeAppState.rooms[room][device] ? (
                    <span style={{ color: "green" }}>On</span>
                  ) : (
                    <span style={{ color: "red" }}>Turning off...</span>
                ) : !tentativeAppState.rooms[room][device] ? (
                  <span style={{ color: "red" }}>Off</span>
                ) : (
                  <span style={{ color: "green" }}>Turning on...</span>

That’s it!

If you created the React app and downloaded the Gist, you should be able to run it, hold the mic button (or hold down the space bar) and try saying combinations of ”turn on”, ”turn off”, ”lights”, ”radio”, ”television” and rooms like ”living room”, ”bedroom” and ”kitchen”.

Hopefully you now have an idea how you can integrate a voice interface to your React app. The next step would be creating something of your own. A good starting point would be thinking of what kind of phrases you’d like to use and sketch them out in Speechly Dashboard.


  • You'll notice that nothing will happen if you leave out a part of the sentence. This example can (and probably should) be improved by allowing the user to specify the key information (the room, device and power state) spread over multiple utterances. This would make the voice experience more flexible and more pleasant to use.
  • alterAppState is very reducer-like. It could actually be a reducer, but it would not be able to directly conjure any side-effects like trigger animations/transitions, although they are not showcased in this example.
  • For multimodal use, the example could be improved by storing setAppState also at the start of a new utterance. The current approach, which uses setAppState only at the end of the utterance will not work gracefully if the widgets were also manipulatable with touch or mouse, as the old app state is restored upon starting a new utterance. Any app state changes made using GUI would be lost.
  • Please note that it's currently possible that the transitional state visualisation may go unnoticed if the tentative period is very short. Improved visualisation may use something like react-spring to launch a clearly visible effect upon a state change, which would ensure that the user has the time to see it.
  • If you're interested, there's an article specifically about guidelines for high productivity voice apps here.

Happy hacking!


About Speechly

Speechly is a YC backed company building tools for speech recognition and natural language understanding. Speechly offers flexible deployment options (cloud, on-premise, and on-device), super accurate custom models for any domain, privacy and scalability for hundreds of thousands of hours of audio.

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