JavaScript 数字NaN属性

JavaScript 数字NaN属性

<html>
   <head>

      <script type = "text/javascript">
         <!--
            function showValue() {
               var dayOfMonth = 50;

               if (dayOfMonth < 1 || dayOfMonth > 31) {
                  dayOfMonth = Number.NaN
                  alert("Day of Month must be between 1 and 31.")
               }
               Document.write("Value of dayOfMonth : " + dayOfMonth );
            }
         //-->
      </script>

   </head>

   <body>
      <p>Click the following to see the result:</p>

      <form>
         <input type = "button" value = "Click Me" onclick = "showValue();" />
      </form>

   </body>
</html>