Javascript code that can verify if special characters are used in a textbox

In the event that you would like to use client-side code to (1) inform a user that he/she has entered invalid characters in a textbox control, (2) highlight that control, and (3) place the focus on it, the following Javascript code can be added to a validation function to carry out all of three of those actions:

function ValidateRequest()
{
...
   if (form.userinput_textbox.value != 0)

   {
      var userInputField = form.userinput_textbox.value;
      var invalidChars = "/!@#$%^&*(){}[]<>\\";
      for (var i = 0; i < userInputField.length; i++)
      {
         if (invalidChars.indexOf(userInputField.charAt(i)) != -1)
         {
            window.scrollTo(0, 0);
            alert ("Please don't use any special characters or punctuation within the given textbox control."); 
            form.userinput_textbox.backgroundColor = "C6ECFF";
            form.userinput_textbox.focus();
            return false;
         }
      }
   }
...
}