Divers

//JS
var store_exec = new Array();

//store[0] = new Array();
store_exec[0] = new Array([' ', '0']);
store_exec[1] = new Array(<?php echo return_array_JS_us_groupes(); ?>);
store_exec[2] = new Array(<?php echo return_array_JS_users(); ?>);
//store_exec[2] = new Array(['1', 'Chri'], ['2', 'ju']);

function init_exec(formul, firBox, secBox, secVal) {
  var box = formul.elements[firBox];
  if(box.options[box.selectedIndex].value != "0") {
    populate_exec(formul, firBox, secBox, secVal);
  } else {
    return;
  }
  /*  //optionTest = true;
    lgth = formul.elements[secBox].options.length;
    formul.elements[secBox].options[lgth] = null;
    if(formul.elements[secBox].options[lgth]); //optionTest = false;
  } else {

  }
  */
}

function populate_exec(formul, firBox, secBox, secVal) {
  var box = formul.elements[firBox];
  var box2 = formul.elements[secBox];
  var number = box.value;
  if (!number) { number = 0; }
  var list = store_exec[number];
  box2.options.length = 0;
  for(i=0;i<list.length;i++) {
    box2.options[i] = new Option(list[i][1],list[i][0]);
    //if(box2.value == secVal) { box2.options[i].selected = true; }
  }
  box2.value = secVal;  
    //if(box2.value=secVal) { box2.options[i].selected = true; }

}

with <body onLoad="init_exec(document.forms['rendez_vous'], 'id_type_exec', 'id_exec', '0')">

// First box (PHP)
$executant = '<select name="id_type_exec" onChange="populate_exec(document.forms[\'rendez_vous\'], \'id_type_exec\', \'id_exec\', \''.$id_exec.'\')" style="width:150px;">';
$executant .= '<option>Executant</option>';
while($res = mysql_fetch_assoc($exe)) {
  if($res['id_type_exec'] == $id_type_exec) { $sel = 'selected="selected"'; }
  else { $sel = ''; }
  $executant .= '<option value="'.$res['id_type_exec'].'" '.$sel.'>'.$res['libelle'].'</option>';
}
$executant .= '</select>';