<html> <head> <meta charset="utf-8"> <title>JS Bin</title> </head> <body> <form action="insert.php" method="post"> <table> <tr><td id="c1">c1</td><td id="c2">c2</td ><td id="c3">c3</td></tr> <tr><td id="c4">c4</td><td id="c5">c5</td><td id="c3">c3</td></tr> </table> <input type="hidden" id="id_elm" name="id_elm" value=""> <input type='submit' value="go"> </form> </body> </html>
document.getElementById("id_elm").value="La valeur à lui donner...";