TextScramble.js

var letters = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","i","u","v","w","x","y","z","~","&","|","^","ç","@","]","[","{","}","ù","*","µ","¤","$","£","€","°",")","(","+","-","/","<",">","²","`","é","è","1","2","3","4","5","6","7","8","9","0"];
var activeClass = 'is-active';
var wrapperClass = '.js-text-animate-wrapper';
var stringClass = '.js-text-animate';
var charClass = 'char';
var $string = $(wrapperClass);

$string.each(textScramble);

function characterWrap($el) {
  var text = $el.text();
  var chars = text.split('');
  var charsWrap = chars.map(function(char) {
    return '<span class="' + charClass + '" data-char="' + char + '">' + char + '</span>';
  });
  var newText = charsWrap.join('');

  $el.html(newText);
  $el.find('.' + charClass).each(function(index, letter) {
    var $letter = $(letter);
    var letterWidth = $letter.width();

    $letter.css({
      'width': letterWidth,
      'display': 'inline-block',
    });
  });
}

function setRandomChar($el) {
  var randomIndex = parseInt(Math.random() * letters.length - 1);

  $el.text(letters[randomIndex]);
}

function stringAnimate($el) {
  $el.find('.' + charClass).each(function (index, letter) {
    var $letter = $(letter);
    var finalChar = $letter.data('char');
    var animationIndex = 0;
    var speedMin = 100;
    var speedRange = 50;
    var speed = speedMin + (Math.random() * speedRange);

    var interval = requestInterval(function() {
      if (animationIndex <= 4) {
        setRandomChar($letter);
        animationIndex++;
      } else {
        $letter.text(finalChar);
        $letter.attr('style', '');
        clearRequestInterval(interval);
      }
    }, speed);
  });
}

function textScramble(index, wrapper) {
  var $wrapper = $(wrapper);

  var waypoint = new Waypoint({
    element: $wrapper[0],
    handler: function() {
      $wrapper.addClass(activeClass);
      $wrapper.find(stringClass).each(function(index, text) {
        var $text = $(text);

        characterWrap($text);

        $text.find('.' + charClass).each(function (index, letter) {
          var $letter = $(letter);
          setRandomChar($letter);
        });

        stringAnimate($text);
      });

      waypoint.destroy();
    },
    offset: '75%',
  });
}

Beware uses jQuery. Need to rewrite into vanilla.