JavaScript 就是数的平方根

JavaScript 就是数的平方根

<html>
   <head>
      <title>Calculate root</title>
   </head>

   <body>
      <script>
         function displayRoot(x, num) {
            val = num % 2;
            if((val == 1) || x < 0)
            x = -x;
            var a, num;
            a = Math.pow(x, 1 / num);
            num = Math.pow(a, num);
            if(Math.abs(x - num) < 1 && (x > 0 === num > 0))
            return val ? -a : a;
         }
         document.write(displayRoot(36, 2));
         document.write("<br>"+displayRoot(49, 2));
         document.write("<br>"+displayRoot(36, -2));
         document.write("<br>"+displayRoot(216, -2));
      </script>
   -+
   </body>
</html>