老师帮我看看代码，需要改善吗？

来源：3-31 编程练习

慕妹8524794

2019-11-04 02:12:27

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>首字母变大写</title>
</head>
<body>
<script>
    //补充代码
    var str = "all time is no time when it is past";
  function toUpper (value){
   var arr = value.split(" ");
   var num= " ";
   for (var i = 0; i < arr.length; i++){
    var Upp = arr[i].charAt(0);
    num += Upp.toUpperCase()+arr[i].substr(1)+ " ";
   }
   return num;
  }
  document.write(toUpper(str));
</script>
</body>
</html>