问如何创造一个平滑的类型效果？JS

EN

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

jQuery(document).ready(function($) {
  //set animation timing
  var animationDelay = 2500,
    //loading bar effect
    barAnimationDelay = 3800,
    barWaiting = barAnimationDelay - 3000, //3000 is the duration of the transition on the loading bar - set in the scss/css file
    //letters effect
    lettersDelay = 50,
    //type effect
    typeLettersDelay = 150,
    selectionDuration = 500,
    typeAnimationDelay = selectionDuration + 800,
    //clip effect 
    revealDuration = 600,
    revealAnimationDelay = 1500;

  initHeadline();


  function initHeadline() {
    //insert <i> element for each letter of a changing word
    singleLetters($('.cd-headline.letters').find('b'));
    //initialise headline animation
    animateHeadline($('.cd-headline'));
  }

  function singleLetters($words) {
    $words.each(function() {
      var word = $(this),
        letters = word.text().split(''),
        selected = word.hasClass('is-visible');
      for (i in letters) {
        if (word.parents('.rotate-2').length > 0) letters[i] = '<em>' + letters[i] + '</em>';
        letters[i] = (selected) ? '<i class="in">' + letters[i] + '</i>' : '<i>' + letters[i] + '</i>';
      }
      var newLetters = letters.join('');
      word.html(newLetters).css('opacity', 1);
    });
  }

  function animateHeadline($headlines) {
    var duration = animationDelay;
    $headlines.each(function() {
      var headline = $(this);

      if (headline.hasClass('loading-bar')) {
        duration = barAnimationDelay;
        setTimeout(function() {
          headline.find('.cd-words-wrapper').addClass('is-loading')
        }, barWaiting);
      } else if (headline.hasClass('clip')) {
        var spanWrapper = headline.find('.cd-words-wrapper'),
          newWidth = spanWrapper.width() + 10
        spanWrapper.css('width', newWidth);
      } else if (!headline.hasClass('type')) {
        //assign to .cd-words-wrapper the width of its longest word
        var words = headline.find('.cd-words-wrapper b'),
          width = 0;
        words.each(function() {
          var wordWidth = $(this).width();
          if (wordWidth > width) width = wordWidth;
        });
        headline.find('.cd-words-wrapper').css('width', width);
      };

      //trigger animation
      setTimeout(function() {
        hideWord(headline.find('.is-visible').eq(0))
      }, duration);
    });
  }

  function hideWord($word) {
    var nextWord = takeNext($word);

    if ($word.parents('.cd-headline').hasClass('type')) {
      var parentSpan = $word.parent('.cd-words-wrapper');
      parentSpan.addClass('selected').removeClass('waiting');
      setTimeout(function() {
        parentSpan.removeClass('selected');
        $word.removeClass('is-visible').addClass('is-hidden').children('i').removeClass('in').addClass('out');
      }, selectionDuration);
      setTimeout(function() {
        showWord(nextWord, typeLettersDelay)
      }, typeAnimationDelay);

    } else if ($word.parents('.cd-headline').hasClass('letters')) {
      var bool = ($word.children('i').length >= nextWord.children('i').length) ? true : false;
      hideLetter($word.find('i').eq(0), $word, bool, lettersDelay);
      showLetter(nextWord.find('i').eq(0), nextWord, bool, lettersDelay);

    } else if ($word.parents('.cd-headline').hasClass('clip')) {
      $word.parents('.cd-words-wrapper').animate({
        width: '2px'
      }, revealDuration, function() {
        switchWord($word, nextWord);
        showWord(nextWord);
      });

    } else if ($word.parents('.cd-headline').hasClass('loading-bar')) {
      $word.parents('.cd-words-wrapper').removeClass('is-loading');
      switchWord($word, nextWord);
      setTimeout(function() {
        hideWord(nextWord)
      }, barAnimationDelay);
      setTimeout(function() {
        $word.parents('.cd-words-wrapper').addClass('is-loading')
      }, barWaiting);

    } else {
      switchWord($word, nextWord);
      setTimeout(function() {
        hideWord(nextWord)
      }, animationDelay);
    }
  }

  function showWord($word, $duration) {
    if ($word.parents('.cd-headline').hasClass('type')) {
      showLetter($word.find('i').eq(0), $word, false, $duration);
      $word.addClass('is-visible').removeClass('is-hidden');

    } else if ($word.parents('.cd-headline').hasClass('clip')) {
      $word.parents('.cd-words-wrapper').animate({
        'width': $word.width() + 10
      }, revealDuration, function() {
        setTimeout(function() {
          hideWord($word)
        }, revealAnimationDelay);
      });
    }
  }

  function hideLetter($letter, $word, $bool, $duration) {
    $letter.removeClass('in').addClass('out');

    if (!$letter.is(':last-child')) {
      setTimeout(function() {
        hideLetter($letter.next(), $word, $bool, $duration);
      }, $duration);
    } else if ($bool) {
      setTimeout(function() {
        hideWord(takeNext($word))
      }, animationDelay);
    }

    if ($letter.is(':last-child') && $('html').hasClass('no-csstransitions')) {
      var nextWord = takeNext($word);
      switchWord($word, nextWord);
    }
  }

  function showLetter($letter, $word, $bool, $duration) {
    $letter.addClass('in').removeClass('out');

    if (!$letter.is(':last-child')) {
      setTimeout(function() {
        showLetter($letter.next(), $word, $bool, $duration);
      }, $duration);
    } else {
      if ($word.parents('.cd-headline').hasClass('type')) {
        setTimeout(function() {
          $word.parents('.cd-words-wrapper').addClass('waiting');
        }, 200);
      }
      if (!$bool) {
        setTimeout(function() {
          hideWord($word)
        }, animationDelay)
      }
    }
  }

  function takeNext($word) {
    return (!$word.is(':last-child')) ? $word.next() : $word.parent().children().eq(0);
  }

  function takePrev($word) {
    return (!$word.is(':first-child')) ? $word.prev() : $word.parent().children().last();
  }

  function switchWord($oldWord, $newWord) {
    $oldWord.removeClass('is-visible').addClass('is-hidden');
    $newWord.removeClass('is-hidden').addClass('is-visible');
  }
});

.cd-intro {
  margin: 4em auto;
}
@media only screen and (min-width: 768px) {
  .cd-intro {
    margin: 5em auto;
  }
}
@media only screen and (min-width: 1170px) {
  .cd-intro {
    margin: 6em auto;
  }
}
.cd-headline {
  font-size: 3rem;
  line-height: 1.2;
}
@media only screen and (min-width: 768px) {
  .cd-headline {
    font-size: 4.4rem;
    font-weight: 300;
  }
}
@media only screen and (min-width: 1170px) {
  .cd-headline {
    font-size: 6rem;
  }
}
.cd-words-wrapper {
  display: inline-block;
  position: relative;
  text-align: left;
}
.cd-words-wrapper b {
  display: inline-block;
  position: absolute;
  white-space: nowrap;
  left: 0;
  top: 0;
}
.cd-words-wrapper b.is-visible {
  position: relative;
}
.no-js .cd-words-wrapper b {
  opacity: 0;
}
.no-js .cd-words-wrapper b.is-visible {
  opacity: 1;
}
/* -------------------------------- 

xclip 

-------------------------------- */

.cd-headline.clip span {
  display: inline-block;
  padding: .2em 0;
}
.cd-headline.clip .cd-words-wrapper {
  overflow: hidden;
  vertical-align: top;
}
.cd-headline.clip .cd-words-wrapper::after {
  /* line */
  content: '';
  position: absolute;
  top: 0;
  right: 0;
  width: 2px;
  height: 100%;
  background-color: #aebcb9;
}
.cd-headline.clip b {
  opacity: 0;
}
.cd-headline.clip b.is-visible {
  opacity: 1;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="header-caption" id="page-top">
  <!-- type headline start-->
  <h3 class="cd-headline clip is-full-width">
    <span>I'm </span>
    <span class="cd-words-wrapper" style="width: 178px;">
      <b class="is-visible">David.</b>
      <b class="is-hidden"> Professional Designer.</b>
      <b class="is-hidden">Admin Assistant .</b>
    </span>
  </h3>
  <!-- type headline end -->
</div>