#MonthOfCode - Day 1: hello world

My entry for the 1st day of the month of code. The theme for today is: hello world.

Code after the break.

hello-world.jsview raw
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(function() {

  var el = document.getElementById('moc-1');
  var source = '#monthofcode';
  var target = 'hello world!';
  var alphabet = 'abcdefghijklmnopqrstuvwxyz0123456789#! ';

  function animate(src, tgt, done) {
    function step() {
      if (src === tgt) {
        return done();
      }
      var nextSrc = '';
      for (var i = 0; i < src.length; i++) {
        // increment each letter if target not reached
        if (src.charAt(i) !== tgt.charAt(i)) {
          var nextIndex = alphabet.indexOf(src.charAt(i)) + 1;
          nextIndex %= alphabet.length;
          nextSrc += alphabet.charAt(nextIndex);
        } else {
          nextSrc += src.charAt(i);
        }
      }
      el.innerHTML = nextSrc;
      src = nextSrc;
      setTimeout(step, 120);
    }
    step();
  }

  function run() {
    animate(source, target, function done() {
      // swap target and source for next iteration
      var tmp = source;
      source = target;
      target = tmp;

      setTimeout(run, 2000);
    });
  }
  run();

})();