<h1>Loop</h1>
<ul>
<script>
    document.write('<li>1</li>');
    var i = 0;
    while(i < 3){
      document.write('<li>2</li>');
      document.write('<li>3</li>');
      i = i + 1;
    }
    document.write('<li>4</li>');
</script>