Text 2 Speech.js

(function(Scratch) {
  'use strict';

  class Tools {
    getInfo () {
      return {
        id: 'wpstudio01tts',
        name: 'System Text To Speech',
        blocks: [
          {
            opcode: 'speak',
            blockType: Scratch.BlockType.COMMAND,
            text: 'speak [TEXT]',
            arguments: {
              TEXT: {
                type: Scratch.ArgumentType.STRING,
                defaultValue: 'Hello'
              }
            }
          }
        ]
      };
    }

    speak (args) {
      return new Promise((resolve, reject) => {
        const utterance = new SpeechSynthesisUtterance(args.TEXT);
        utterance.onend = () => {
          resolve();
        };
        utterance.onerror = () => {
          reject(new Error('Utterance error'));
        };
        speechSynthesis.speak(utterance);
      });
    }
  }

  Scratch.extensions.register(new Tools());
})(Scratch);