type the Sting one by one and backward also we want to delete one by one

<p id="demo"></p>
<script>
  var i = 0;var txt = 'Lorem ipsum dummy text blabla.';var speed =100,speedg=80,speedgg=800;function typeWriter(){if (i < txt.length){    document.getElementById("demo").innerHTML += txt.charAt(i);i++;}else{document.getElementById("demo").innerHTML="";i=0;}setTimeout(typeWriter, speed);}typeWriter();
</script>