type-text.js

(function (id) {
  'use strict';

  var container = document.getElementById(id);

  if (!container) {
    console.warn('No keep-it-on element found on page.');
  }

  var text = container.textContent.trim();

  container.textContent = '';

  var index = 0;

  createCharacterPromise(index).then(iterateText);

  function iterateText() {
    index++;
    if (index < text.length) {
      createCharacterPromise(index).then(x);
    } else {
      console.log('written');
    }
  }

  function createCharacterPromise(index) {
    return new Promise(function (resolve, reject) {
      setTimeout(function () {
        appendCharacterToText(text[index]);
        resolve(index);
      }, generateRandomInteger(30, 100));
    });
  }


  function generateRandomInteger(min, max) {
    min = Math.ceil(min);
    max = Math.floor(max);
    return Math.floor(Math.random() * (max - min)) + min;
  }

  function appendCharacterToText(character) {
    container.textContent += character;
    return character.charAt();
  }
})('keep-it-on');