Field Content Validation

Ok, I've had several people email me wanting to know how they can validate a field based on a certain criteria.  Well, I through this together and hope it will work for you.  There are many ways to do this such as Regular Expression, and other functions, but you should be able to implement this rather easily.

function validate_char(field) {
 var valid = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
 var ok = "yes";
 var temp;
 for (var i=0; i<field.value.length; i++) {
   temp = "" + field.value.substring(i, i+1);
   if (valid.indexOf(temp) == "-1") ok = "no";
 }
 if (ok == "no") {
   alert("Invalid entry!  Only characters Aa-Zz are accepted!");
   field.focus();
   field.select();
 }
}

Now just simply call this like:

<INPUT type="text" name="txt_name" onBlur="validate_char(this)">

Feel free to change the valid variable to anything you'd like to restrict user input.