console 命令行工具 X clear
console
<!DOCTYPE html>
<html >
  <head>
    <meta charset="UTF-8" />
    <title></title>
  </head>
    <script>
      function Reverse(str)
      {
        var arr =[];
        for(var i=str.length-1;i>=0;i--)
        {
           arr.push(str[i]);
        }
        return arr.join("");
      }
      document.write(Reverse('abcde'));
      document.write("<br />") 
    </script>
</html>