watson-speech/speech-to-text/writable-element-stream.js

IBM Watson Speech to Text and Text to Speech SDK for web browsers.

'use strict';

var { Writable } = require('readable-stream');
var util = require('util');
var defaults = require('defaults');

/**
 * Writable stream that accepts results in either object or string mode and outputs the text to a supplied html element
 *
 * Can show interim results when in objectMode
 *
 * @param {Object} options
 * @param {String|DOMElement} options.outputElement
 * @param {String} [options.property] what property of the element should the text be set to. Defaults to `value` for `<input>`s and `<textarea>`s, `textContent` for everything else
 * @param {Boolean} [options.clear=true] delete any previous text
 * @constructor
 */
function WritableElementStream(options) {
  this.options = options = defaults(options, {
    decodeStrings: false, // false = don't convert strings to buffers before passing to _write (only applies in string mode)
    property: null,
    clear: true
  });

  this.el = typeof options.outputElement === 'string' ? document.querySelector(options.outputElement) : options.outputElement;

  if (!this.el) {
    throw new Error('Watson Speech to Text WritableElementStream: missing outputElement');
  }

  Writable.call(this, options);

  // for most elements we set the textContent, but for form elements, the value property is probably the expected target
  var propMap = {
    INPUT: 'value',
    TEXTAREA: 'value'
  };
  this.prop = options.property || propMap[this.el.nodeName] || 'textContent';

  if (options.clear) {
    this.el[this.prop] = '';
  }

  if (options.objectMode) {
    this.finalizedText = this.el[this.prop];
    this._write = this.writeObject;
  } else {
    this._write = this.writeString;
  }
}
util.inherits(WritableElementStream, Writable);

WritableElementStream.prototype.writeString = function writeString(text, encoding, next) {
  this.el[this.prop] += text;
  next();
};

WritableElementStream.prototype.writeObject = function writeObject(data, encoding, next) {
  if (Array.isArray(data.results)) {
    data.results.forEach(function(result) {
      if (result.final) {
        this.finalizedText += result.alternatives[0].transcript;
        this.el[this.prop] = this.finalizedText;
      } else {
        this.el[this.prop] = this.finalizedText + result.alternatives[0].transcript;
      }
    }, this);
  }
  next();
};

module.exports = WritableElementStream;