<? 
 
printf("<SCRIPT LANGUAGE=\"JavaScript\"> 
<!-- 
 
<!-- Begin 
function CheckAll(chk) 
	{ 
	if(document.testformular.mastercheckbox_1.checked) 
		{ 
		for (i = 0; i < chk.length; i++) 
			{ 
			chk[i].checked = true ; 
			} 
		} 
	else 
		{ 
		for (i = 0; i < chk.length; i++) 
			{ 
			chk[i].checked = false ; 
			} 
		} 
	} 
</script> 
"); 
 
 
$_db_result_tiere = array("Hund", "Katze", "Maus"); 
$_db_result_besitz = array("Villa", "Porsche", "Yacht"); 
 
printf("<form name=\"testformular\" action=\"%s\" method=\"post\">", $_SERVER['PHP_SELF']); 
printf("Alle markieren: <input type=\"checkbox\" id=\"mastercheckbox_1\" onClick=\"CheckAll(document.testformular.childcheckbox_1)\">"); 
foreach($_db_result_tiere as $key=> $value) 
	{ 
	printf("<br><input type=\"checkbox\" id=\"childcheckbox_1\" name=\"tiere_%s\" value=\"1\">%s", $key, $value); 
	} 
 
 
printf("<br>Alle markieren: <input type=\"checkbox\" id=\"mastercheckbox_2\" onClick=\"CheckAll(document.testformular.childcheckbox_2)\">"); 
foreach($_db_result_tiere as $key=> $value) 
	{ 
	printf("<br><input type=\"checkbox\" id=\"childcheckbox_2\" name=\"besitz_%s\" value=\"1\">%s", $key, $value); 
	} 
printf("</form>"); 
?> 

 
function CheckAll(chk, id) 
     { 
     if(document.testformular.id.checked) 
     ... 
     } 
 
... 
CheckAll(document.testformular.childcheckbox_1, this.id) 
... 

Anstatt: 
if(document.testformular.id.checked)  
     ...  
}  
Das hier: 
 
if(document.testformular.elements[id].checked)  
     ...  
}