<script>
var iChars = "`~!@#$%^&*()+=-_:[]\;,./{}|\":<>?'";
    function hasWhiteSpace(s){
     reg = new RegExp(/^\s+$/);
     if (reg.test(s)) {
          alert("Please Check Your Fields For Spaces");
          return false;
     }
     return true;
}  
    function test(){
     var count=document.form.text.value.length;
     for (var i = 0; i < count; i++) {
     if ((iChars.indexOf(document.form.text.value.charAt(i)) != -1)||hasWhiteSpace(document.form.text.value)) 
     {
     alert("Contains special characters or whitespace. These are not allowed.");
     document.form.text.value="";
     return false;
      }
    }   
     }
     </script>
     <form name="form" onsubmit="return test();">
     Enter data: <input type="text" name="text">

     <input type="submit" value="submit">
     </pre>
     </form>