how can i know if element is not exists in document

Hello
im trying to know if some html object is on the document
but when i try simple :
alert(document["foo"].id) it even don't alert the alert...
by the way in this example there is no foo object .
so.. how can i know if object is NOT exists??
thanks

Well, becuase you have some illegal syntax there. try something like thisfunction getNode( id )
{
return ( document.all || document.getElementById )( id );
}

alert( getNode( "foo" ) );