Displaying an animation text and fetching first letter of each word to show acronym as animation

var words = document.getElementsByClassName('word');
var wordArray = [];
var currentWord = 0;

words[currentWord].style.opacity = 1;
for (var i = 0; i < words.length; i++) {
  splitLetters(words[i]);
}

function changeWord() {
  var cw = wordArray[currentWord];
  var nw = currentWord == words.length-1 ? wordArray[0] : wordArray[currentWord+1];
  for (var i = 0; i < cw.length; i++) {
    animateLetterOut(cw, i);
  }
  
  for (var i = 0; i < nw.length; i++) {
    nw[i].className = 'letter behind';
    nw[0].parentElement.style.opacity = 1;
    animateLetterIn(nw, i);
  }
  
  currentWord = (currentWord == wordArray.length-1) ? 0 : currentWord+1;
}

function animateLetterOut(cw, i) {
  setTimeout(function() {
    cw[i].className = 'letter out';
  }, i*80);
}

function animateLetterIn(nw, i) {
  setTimeout(function() {
    nw[i].className = 'letter in';
  }, 340+(i*80));
}

function splitLetters(word) {
  var content = word.innerHTML;
  word.innerHTML = '';
  var letters = [];
  for (var i = 0; i < content.length; i++) {
    var letter = document.createElement('span');
    letter.className = 'letter';
    letter.innerHTML = content.charAt(i);
    word.appendChild(letter);
    letters.push(letter);
  }
  
  wordArray.push(letters);
}

changeWord();
setInterval(changeWord, 4000);

@import url(https://fonts.googleapis.com/css?family=Open+Sans:600);

body {
  font-family: 'Open Sans', sans-serif;
  font-weight: 600;
  font-size: 40px;
}

.text {
  position: absolute;
  width: 650px;
  left: 50%;
  margin-left: -400px;
  height: 40px;
  top: 50%;
  margin-top: -20px;
}
span {
    white-space: pre-wrap;
}

p {
  display: inline-block;
  vertical-align: top;
  margin: 0;
}

.word {
  position: absolute;
  width: 420px;
  opacity: 0;
}

.letter {
  display: inline-block;
  position: relative;
  float: left;
  transform: translateZ(25px);
  transform-origin: 50% 50% 25px;
}

.letter.out {
  transform: rotateX(90deg);
  transition: transform 0.32s cubic-bezier(0.55, 0.055, 0.675, 0.19);
}

.letter.behind {
  transform: rotateX(-90deg);
}

.letter.in {
  transform: rotateX(0deg);
  transition: transform 0.38s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.wisteria {
  color: #8e44ad;
}

<div class="text">
  <p>Welcome to </p>
  <p>
    <span class="word wisteria">Dr.Nael Center</span>
   
  </p>
</div>