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speechrecognition with javascript
Christoph LipautzDecember 16, 20174 min read

Using SpeechRecognition via Browser

With no doubt, JavaScript has become an elementary driving force for the Internet resulting in incredibly fast development and great success for the web. A lot of new and interesting JavaScript WebAPIs have become available and many of them are supported by major browsers. In this blog post, we’ll explore the Web Speech API to be used for speech recognition


Progressive enhancement

The speech API is still experimental and may not be available in every user agent or at least not fully working. A common approach for modern websites and web applications is to progressively enhance the user experience, hence using what is available to the user. This design principle is known as progressive enhancement. If you create a web application or a website your own, I strongly recommend starting with implementing a smaller core feature set that supports a wide range of user agents. Then optimize and enhance the user experience using newer technology, keeping a fallback ensured.

In the eyeson JavaScript library, we collect requirements in a single feature detector interface in order to decide whether a user agent can handle a certain functionality or not. As an example, at the time of this writing, Google Chrome requires an extension to handle screen capturing, whereas Mozilla Firefox supports a handy interface to access this functionality. Other user agents won’t have this capability at all. Therefore the feature detector queries for available APIs, asks for the installed extension, and tries to figure out the best setup possible for the end-user.

Back to the Web Speech API, it provides two working modes: Handling Text-to-Speech and SpeechRecognition. We’ll skip the first and build a simple and handy extension for  to control a video conference web GUI with speech input.

Speak My Language

When it comes to speech synthesis it is essential that the language dealt with is known beforehand. In terms of accessibility, a document-level language definition is essential, as assistive technologies using text-to-speech may fall back on the user's default language. Fortunately, this is as simple as setting the lang=attribute in your opening HTML tag, you don’t want your visitor from France listening to a french dialect interpreting your content in English.

In our case, we don’t want to concentrate too much on the content but the input via the user's voice. The API provides us with a configuration to set the user's language, if none is provided will use the HTML documents lang attribute. In most cases this will be fine, there’s definitely room for improvement here. Having British users dealing with language settings en-GB instead of en-US will result in surprisingly better matches and therefore a better user experience.

Interim Results, Grammar, and other Options

Although speech recognition is quite a complex topic, the current specification has a short and powerful set of properties. Let’s have a short look at some of the setting options provided.

When to Use

With popular voice recognition assistants like Alexa, Siri, or OK Google your users might already be used to speech control. The use of this technology can improve accessibility to a wide range of your users significantly. Additionally, there are scenarios where there’s simply no other input mechanism available, think of remote support using a headset requiring both hands to be free in order to get a job done.

If you do provide voice control, ensure your user is aware of it and what commands are available.

Coding Example

The following code snippets provides a fully working example that can be used to extend the video conferencing web app with speech recognition voice control. The eyeson JavaScript library uses event handling to interact with the video communications system, providing a simple interface for developers. We’ll use the toogle_video event in order to mute our camera and make it active again on voice command ninja (ref).

As described we try to use any SpeechRecognition inside the initialization method, or fallback on not sticking any further with this feature. If we successfully detect the API to be available, we configure it to skip interim results, stick with one result and provide continuous recognition.

We use onresult to attach an input handler, and start listening. Within a received result, we’re just interested in the transcript interpreted by our recognition - a received ‘ninja’ will get our attention and the input handler receives the video toggle event, switching between mute and unmute state.

 * Handle speech input. 
class SpeechControl {
  constructor(handler) {
    this.handler = handler;

    if (this.init()) {
      this.recognition.onresult = this.handleInput.bind(this);
      console.debug('recognition start...');

  init() {
    this.recognition = new (window.SpeechRecognition ||
      window.webkitSpeechRecognition || window.mozSpeechRecognition ||
      window.oSpeechRecognition || window.msSpeechRecognition)();
    if (!this.recognition) {
      return false;

    this.recognition.interimResults = false;
    this.recognition.maxAlternatives = 1;
    this.recognition.continuous = true;
    return true;

  handleInput(event) {
    const sentence = event.results[event.results.length - 1][0];
    console.debug('** RECEIVED **', sentence.transcript);
    if (sentence.transcript.toLowerCase().trim() === 'ninja') {
      console.debug('** NINJA **');
      this.handler && this.handler({ type: 'toggle_video' });
 export default SpeechControl;

Browser Support

Note that the speech recognition web API is fully available only in Google Chrome. A specification draft version is created and published for W3C. Firefox and Opera web browsers ship with the support as well but require a manual change of configuration flags in order to enable the feature.


Although speech recognition might not have full support for every user agent, it might be available for users who want or even need to use it. This powerful but easy to handle control mechanism might give your website or web application a head start to the upcoming trend of interacting with software via voice.