Typing text transition

  <p id="offscreen-text" class="offscreen-text"></p>
  <p id="text" class="text"></p>
  
  <svg id="svg">
  </svg>
  
  <input type="text" class="input", id="input" />

  <script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/1.20.3/plugins/CSSPlugin.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/1.20.3/easing/EasePack.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/1.20.3/TweenLite.min.js"></script>

html, body {
  width: 100%;
  height: 100%;
  overflow: hidden;
  font-family: 'Rubik Mono One', sans-serif;
  background: #22292C;
}

svg {
  width: 100%;
  height: 100%;
  position: absolute;
  top: 0px;
  left: 0px;
  z-index: 0;
}

.input {
  position: absolute;
  z-index: 1;
  bottom: 0px;
  font-size: 20px;
  text-align: center;
  left: 50%;
  transform: translateX(-50%);
  font-family: helvetica, sans-serif;
  bottom: 20px;
  background: none;
  border: 1px solid #ddd;
  color: #eee;
}

.text, .offscreen-text {
  width: 100%;
  top: 50%;
  transform: translateY(-50%);
  display: block;
  position: absolute;
  margin: 0;
}

.offscreen-text {
  text-align: center;
  top: -9999px;
}

.text span {
  position: absolute;
}

const selectSVG = id => {
  const el = document.getElementById(id);
  return new SVGElement(el);
};

const createSVG = type => {
  const el = document.createElementNS('http://www.w3.org/2000/svg', type);
  return new SVGElement(el);
};

class SVGElement {
  constructor(element) {
    this.element = element;
  }

  set(attributeName, value) {
    this.element.setAttribute(attributeName, value);
  }

  style(property, value) {
    this.element.style[property] = value;
  }
}

const colors = [
  { main: '#FBDB4A', shades: ['#FAE073', '#FCE790', '#FADD65', '#E4C650'] },
  { main: '#F3934A', shades: ['#F7B989', '#F9CDAA', '#DD8644', '#F39C59'] },
  { main: '#EB547D', shades: ['#EE7293', '#F191AB', '#D64D72', '#C04567'] },
  { main: '#9F6AA7', shades: ['#B084B6', '#C19FC7', '#916198', '#82588A'] },
  { main: '#5476B3', shades: ['#6382B9', '#829BC7', '#4D6CA3', '#3E5782'] },
  { main: '#2BB19B', shades: ['#4DBFAD', '#73CDBF', '#27A18D', '#1F8171'] },
  { main: '#70B984', shades: ['#7FBE90', '#98CBA6', '#68A87A', '#5E976E'] }
];
const svg = selectSVG('svg');
const text = document.getElementById('text');
const offscreenText = document.getElementById('offscreen-text');
const input = document.getElementById('input');
let width = window.innerWidth;
let height = window.innerHeight;
let textSize = 0;
let textCenter = 0;
const letters = [];
const prompt = ['s', 't', 'a', 'r', 't', ' ', 't', 'y', 'p', 'i', 'n', 'g'];
let runPrompt = true;

const resizePage = () => {
  width = window.innerWidth;
  height = window.innerHeight;
  svg.set('height', height);
  svg.set('width', width);
  svg.set('viewBox', `0 0 ${width} ${height}`);
  resizeLetters();
}

const resizeLetters = () => {
  textSize = width / (letters.length+2);
  if (textSize > 100) textSize = 100;
  text.style.fontSize = `${textSize}px`;
  text.style.height = `${textSize}px`;
  text.style.lineHeight = `${textSize}px`;
  offscreenText.style.fontSize = `${textSize}px`;
  const textRect = text.getBoundingClientRect();
  textCenter = textRect.top + textRect.height/2;
  positionLetters();
};

const positionLetters = () => {
  letters.forEach(letter => {
    const timing = letter.shift ? 0.1 : 0;
    TweenLite.to(letter.onScreen, timing, {x:letter.offScreen.offsetLeft+'px', ease: Power3.easeInOut});
    letter.shift = true;
  });
}

const animateLetterIn = letter => {
  const yOffset = (0.5+Math.random()*0.5) * textSize;
  TweenLite.fromTo(letter, 0.4, {scale:0}, {scale:1, ease: Back.easeOut});
  TweenLite.fromTo(letter, 0.4, {opacity:0}, {opacity: 1, ease: Power3.easeOut});
  TweenLite.to(letter, 0.2, {y:-yOffset, ease: Power3.easeInOut});
  TweenLite.to(letter, 0.2, {y:0, ease: Power3.easeInOut, delay: 0.2});
  const rotation = -50 + Math.random()*100;
  TweenLite.to(letter, 0.2, {rotation: rotation, ease: Power3.easeInOut});
  TweenLite.to(letter, 0.2, {rotation: 0, ease: Power3.easeInOut, delay: 0.2});
}

const addDecor = (letter, color) => {
  setTimeout(() => {
    var rect = letter.getBoundingClientRect();
    const x0 = letter.offsetLeft + letter.offsetWidth/2;
    const y0 = textCenter - textSize*0.5;
    const shade = color.shades[Math.floor(Math.random()*4)];
    for (var i = 0; i < 8; i++) addTri(x0, y0, shade);
    for (var i = 0; i < 8; i++) addCirc(x0, y0);
  }, 150);
};

const addTri = (x0, y0, shade) => {
  const tri = createSVG('polygon');
  const a = Math.random();
  const a2 = a + (-0.2 + Math.random()*0.4);
  const r = textSize*0.52;
  const r2 = r + textSize*Math.random()*0.2;
  const x = x0 + r * Math.cos(2 * Math.PI * a);
  const y = y0 + r * Math.sin(2 * Math.PI * a);
  const x2 = x0 + r2 * Math.cos(2 * Math.PI * a2);
  const y2 = y0 + r2 * Math.sin(2 * Math.PI * a2);
  const triSize = textSize * 0.1;
  const scale = 0.3 + Math.random()*0.7;
  const offset = triSize*scale;
  tri.set('points', `0,0 ${triSize*2},0 ${triSize},${triSize*2}`);
  tri.style('fill', shade);
  svg.element.appendChild(tri.element);
  TweenLite.fromTo(tri.element, 0.6, {rotation: Math.random()*360, scale: scale, x: x-offset, y: y-offset, opacity: 1}, {x: x2-offset, y: y2-offset, opacity: 0, ease: Power1.easeInOut, onComplete: () => {
    svg.element.removeChild(tri.element);
  }});
}

const addCirc = (x0, y0) => {
  const circ = createSVG('circle');
  const a = Math.random();
  const r = textSize*0.52;
  const r2 = r + textSize;
  const x = x0 + r * Math.cos(2 * Math.PI * a);
  const y = y0 + r * Math.sin(2 * Math.PI * a);
  const x2 = x0 + r2 * Math.cos(2 * Math.PI * a);
  const y2 = y0 + r2 * Math.sin(2 * Math.PI * a);
  const circSize = textSize * 0.05 * Math.random();
  circ.set('r', circSize);
  circ.style('fill', '#eee');
  svg.element.appendChild(circ.element);
  TweenLite.fromTo(circ.element, 0.6, {x: x-circSize, y: y-circSize, opacity: 1}, {x: x2-circSize, y: y2-circSize, opacity: 0, ease: Power1.easeInOut, onComplete: () => {
    svg.element.removeChild(circ.element);
  }});
}

const addLetter = (char, i) => {
  const letter = document.createElement('span');
  const oLetter = document.createElement('span');
  letter.innerHTML = char;
  oLetter.innerHTML = char;
  text.appendChild(letter);
  const color = colors[i%colors.length];
  letter.style.color = color.main;
  offscreenText.appendChild(oLetter);
  letters[i] = {offScreen: oLetter, onScreen: letter, char: char};
  animateLetterIn(letter);
  addDecor(oLetter, color);
}

const addLetters = value => {
  value.forEach((char, i) => {
    if (letters[i] && letters[i].char !== char) {
      letters[i].onScreen.innerHTML = char;
      letters[i].offScreen.innerHTML = char;
      letters[i].char = char;
    }
    if (letters[i] === undefined) {
      addLetter(char, i);
    }
  });
};

const animateLetterOut = (letter, i) => {
  TweenLite.to(letter.onScreen, 0.1, {scale: 0, opacity: 0, ease: Power2.easeIn, onComplete: () => {
    console.log('removing');
    console.log(letter);
    offscreenText.removeChild(letter.offScreen);
    text.removeChild(letter.onScreen);
    positionLetters();
  }});
  letters.splice(i, 1);
}

const removeLetters = value => {
  for (let i = letters.length-1; i >= 0; i--) {
    const letter = letters[i];
    if (value[i] === undefined) {
      animateLetterOut(letter, i)
    }
  }
}

const onInputChange = () => {
  const value = input.value === '' ? [] : input.value.toLowerCase().split('');
  addLetters(value);
  removeLetters(value);
  resizeLetters();
};

const keyup = (e) => {
  if (runPrompt) {
    input.value = '';
    runPrompt = false;
  };
  onInputChange();
}

const addPrompt = (i) => {
  setTimeout(() => {
    if (runPrompt && prompt[i]) {
      input.value = input.value + prompt[i];
      onInputChange();
      addPrompt(i+1);
    }
  }, 300);
}
  
resizePage();
window.addEventListener('resize', resizePage);
input.addEventListener('keyup', keyup);
input.focus();
addPrompt(0);