[trikadin]

<div id="div"><a id="a" href="javascript: void()">Ссылка</a></div>
<script>
a= document.getElementById("a");
div= document.getElementById("div");
while(a=a.parentNode)
 {
  if (a === div) {
   alert("'a' in 'div'");
   break;
  };
 };
</script>