<script>
   var parent_Func = undefined;
   function call_parent_Func(){
    if(typeof parent_Func != 'undefined'){
     parent_Func();
    }else{
     alert('자식창 함수 호출 실패!')
    }
   }
   function parent_call_parent_Func(){
     alert('부모창 함수 호출 성공!')
   }
</script>

<button onclick="call_parent_Func();">Access function</button>
<iframe id="IDIframe" src="자식창.html"></iframe>

<script>
   function child_Func(){
    alert('자식창 함수 호출 성공!')
   }

   parent.parent_Func = child_Func;
</script>

<button onclick="parent.parent_call_parent_Func();">Access parent function</button>