Adding pause and play functionality to Speech Synthesis API

Question

I'm new to JavaScript and I am trying to add a pause button by linking a button to synth.pause(speakText); where const synth = window.speechSynthesis; and const speakText = new SpeechSynthesisUtterance(textInput.value);.

I can't make speakText accessible to the pause function since I construct my speakText object in my speak() function. I tried making speakText a global variable by calling its constructor outside of the function but that causes speak() to throw an error.

Any idea on how I can achieve this?

JS Code:

//Speak
const speak = () => {
  //Check to see if already speaking
  if (synth.speaking && state === "play") {
    console.error("Already speaking");
    state = "paused";
    console.log("state: " + state);
    return;
  }
  //Make sure there is some input
  if (textInput.value !== "" && state === "stop") {
    const speakText = new SpeechSynthesisUtterance(textInput.value);
    state = "play";

    //Speak error
    speakText.onerror = e => {
      console.log("Something went wrong!");
    };

    //Selected voice
    const selectedVoice = voiceSelect.selectedOptions[0].getAttribute(
      "data-name"
    );

    //Loop through voices to set the correct voice
    voices.forEach(voice => {
      if (selectedVoice === voice.name) {
        speakText.voice = voice;
      }
    });

    //Set the rate and pitch
    speakText.rate = rate.value;
    speakText.pitch = pitch.value;

    //Speak end
    speakText.onend = e => {
      console.log("Done Speaking");
      state = "stop";
    };

    speakController(speakText);
  }
};

const speakController = speakText => {
  console.log("state: " + state);
  if (state === "play") {
    synth.speak(speakText);
  } else if (state === "pause") {
    synth.pause(speakText);
  } else if (state === "stop") {
    synth.cancel(speakText);
  }
};

//----------EVENT LISTENERS----------
var state = "stop";

// Text form submit
textForm.addEventListener("submit", e => {
  e.preventDefault();
  speak();
  textInput.blur();
});

//Pause button
pauseButton.addEventListener("onClick", e => {
  e.preventDefault();
  speakController;
});

user_5217142 · Answer

[..How..] to add a pause button by linking a button to synth.pause(speakText);

The cheap answer would be to have the button call speechSynthesis.pause() (which doesn't take arguments) - because synth is just a copy of the global window.speechSynthesis property.

A better solution is to create a controller that exposes an interface of methods and properties to outside callers, and encapsulates its own internal workings.

You touched on the problem here:

I can't make speakText accessible to the pause function since I construct my speakText object in my speak() function.

which means there's a code structure design issue. But there is another problem: the speech synthesizer doesn't have states of "play", "pause" and "stop". It has two mutually exclusive states of "play" and "pause", and a totally independent condition of "queue empty".

I don't propose to fix the posted code - although I certainly tried. Here's what I ended up with to determine what was going on - it is experimental code but hopefully the podcast will help!

"use strict";
const tr = {
 queue: null,
 pause: null,
 play:  null,
 cancel:  null,
 defaultRate: 1.1,
 defaultPitch: 1,
 // voice selection to do;
};
function createTextReader( tr) {
 let synth = window.speechSynthesis; // abbreviation
 let Utter = SpeechSynthesisUtterance; // abbreviation
 // queue
 tr.queue = (text, rate, pitch, voiceIndex) => {
  let utter = new Utter();
  utter.text = text;
  utter.rate = rate || tr.defaultRate || 1;
  utter.pitch = pitch || tr.defaultPitch || 1;
  // voice selection to do
  // if( voiceParam) ....
  synth.speak( utter);
 };
 tr.pause = () => synth.pause();
 tr.play = () => synth.resume();
 tr.cancel = () => synth.cancel();
}
window.addEventListener( "DOMContentLoaded", function (e) {
createTextReader( tr)}, false);
window.addEventListener("unload", e=>tr.cancel(), false);

Press "queue text" to add text area content to the text reader. Press it multiple times to add text more than once. Press "pause" to pause reading. Press "play" to start or resume reading queued text from the speech synthesizer's fifo queue. Play mode is in effect at startup - but you could pause the reader before queuing text. Press "cancel" to stop reading and empty the queue. It does not change pause versus play mode. If the reader is paused when cancel is clicked, it remains so afterwards. This voice is the default voice in this browser, and may be different in another. More code is needed for voice selection. If you visit MDN's speech synthesis example on git hub, view page source and click on the link to "script.js" you can see how they do it. Oh, and don't forget to cancel speech synthesis on window unload. Thanks for listening!

The link for the MDN page referred to is https://mdn.github.io/web-speech-api/speak-easy-synthesis/

Adding pause and play functionality to Speech Synthesis API

1 Answers