Kontrola vyplněného formuláře

<form action="" method="post" name="FormAA" onsubmit="return AA()">
	<table border="0">
	  <tr>
		<td>aaa:</td>
		<td><input type="text" name="a" size="30" value=""></td>
	  </tr>
	  <tr>
		<td>bbb:</td>
		<td><input type="text" name="b" size="30" value=""> </td>
	  </tr>
	  <tr>
		<td>ccc:</td>
		<td><textarea name="c" rows="5" cols="50"></textarea></td>
	  </tr>
	  <tr>
		<td>ddd:</td>
		<td><textarea name="d" rows="5" cols="50"></textarea></td>
	  </tr>
	</table>
	<input type="submit" value="Uložit">
	<input type="hidden" name="savet" value="1">
</form>

function AA(){
			
	var $a = self.document.forms.FormAA.a.value;
	var $b = self.document.forms.FormAA.b.value;
	var $c = self.document.forms.FormAA.c.value;	
	var $d = self.document.forms.FormAA.d.value;				
	
	if($a == "" || $b == "" || $c == "" || $d == ""){
		alert('Všechny položky označené jako povinné musí být vyplněny');
		return false;
	}else{
		return true;
	}	
}