Validating Form Data and Displaying Graphics with JavaScript

I have not really used JavaScript before but I am trying to validate form elements as they are being filled out. I have an X and a Check mark that I am trying to display next to the field to show if it is valid or not. I know that this is partially right because I can use an alert but I am not sure how to alter the fields of the graphics.

The JavaScript:

function validate_field(field)
{
    var value = document.newAccount.fname;
    if (value==null||value=="")
    {
        document.fnameX.visibility = visible;
        document.fnameOK.visibility = hidden;
       //alert("FAIL");
       return false;
    }
    else
    {
  开发者_JAVA百科      document.fnameX.visibility = hidden;
        document.fnameOK.visibility = visible;
      //alert("TRUE");
      return true;
    }
}

Some of the HTML:

  <form action="XXXXX" method="post" name="newAccount">

    <table width="78%" border="0" align="center">
          <tr>
         <td colspan="2"><strong>Personal Info:</strong> </td>
          </tr>
          <tr>
            <td width="24%"><div align="right">First Name: </div></td>
            <td width="76%">
              <input type="text" onchange="return validate_field(this)"  onfocus="return validate_field(this)" name="fname" tabindex="1" size="50"/> 
              <img name="fnameX" src="redx.jpg" style="visibility:hidden" alt="X" width="18" height="18" /><img name="fnameOK" src="checkmark.jpg" style="visibility:hidden"  alt="Ok" width="18" height="18" /></td>
          </tr>
          <tr>
            <td><div align="right">Last Name: </div></td>
            <td><input type="text" name="lname" tabindex="2" size="50"/></td>
          </tr>
    </table>
    </form>

Your probably better off using CSS classes for something like this.

.valid
{
     padding-right:15px 
     /*or whatever the width of your graphic is*/
     background:url('checkmark.jpg') center right no-repeat; 
     /*remember that the url is relative to the stylesheet*/
}

.invalid
{
     padding-right:15px 
     background:url('redx.jpg') center right no-repeat; 
}

Then your validate function becomes:

function validate_field(field)
{
    var value = field.value;
    if (value==null||value=="")
    {
       field.parentNode.className = 'invalid';
       return false;
    }
    else
    {
       field.parentNode.className = 'valid';
       return true;
    }
}

EDIT:

Remember to keep accessibility in mind, and that unless you are using an alert or making notifications accessible using ARIA attributes users with assistive devices are going to have a tough time with your form.

EDIT:

Here is a working example from your code where I change the background color of the parent table cell of the form input.

EDIT:

And here is an example where I got rid of those not so nice layout tables and replaced them with a fieldset, and modified the Javascript a little bit. If you aren't familiar with jsbin you can append /edit to the url to see/modify the code, like so.