codice:
<html>
    <head>
    <script language="javascript">

     function check()
     {
    for (var i = 0; i < document.myform.elements.length; i++)
        {
     document.myform.elements[i].checked=true ;
        }

     }




    </script>
     <body>
     Link
     <form name="myform">

     <input type="checkbox" name="uno">
     <input type="checkbox" name="due">
     <input type="checkbox" name="tre">
     <input type="checkbox" name="quattro">
     </form>
    </body>
    </html>