Javascript/タイプライター

var text = document.getElementById("text");
var btn = document.getElementById("btn");
var write = document.getElementById("write");
var i = 0;
function w(){
  var t = text.value;
  var s = t.split("");
  write.innerText += s[i];
  i++;
  var st = setTimeout(function(){
  	w()
  }, 300);
  if(i > s.length-1){
  	clearTimeout(st);
  }
}
function f(){
  i = 0;
  text.value = "";
  write.innerText = "";
}