php/javascript help

OK, I almost have a project done, but I am running into a little problem. I need to have a box pop up when the user hits a form button. It should tell how many characters are in the text box. It seems like a simple problem, but I know nothing about javascript. I don't have a clue as to how to pass the variable from the php into the javascript either. For completeness sake I have included the code I currently have. Just as a note, the form dynammically generates a number of entry boxes depending on a count that the user specifies on the previous page. The javascript needs to access the array sequence[] Also, as currently coded it doesn't run. I don't know how to include the javascript so it bombs out when it hits the javascript. Thanks for any help. Keith <? file://orderform.php3 ?> <script language=javascript function generatelength(str) { var mylength = 0; if (!str) return; else { mylength = str.length; alert("The lenght of your sequence is: "+mylenght); } return; } </script> <form action="mailto.php3" method="post"> <table border="0"> <? for ($i = 1; $i <= $number_of_oligos; $i++): ?> <tr> <td> <? echo ("sequence $i") ?> </td> <td> <input type="text" name="sequence[]"><br><br> </td> <td> <input type="button" name="length" value="How long is my sequence?" onClick="generateLength()" <br><br></td> </tr> <? endfor ?> <tr> <td><input type=submit> </tr> </table> </form>