marquee 태그로 랜덤 메시지 표시하기

<script>
function getIdx() {
 var arr = new Array(5);
 arr[0] = "aa";
 arr[1] = "bb";
 arr[2] = "cc";
 arr[3] = "dd";
 arr[4] = "ee";

 var num = Math.floor(Math.random()*4);
 document.getElementById("aa").innerText = arr[num];

}
//setInterval("getIdx()",500);
</script>

<marquee id="aa" behavior="scroll" onfinish="getIdx();" loop="1">가나다라마바사</marquee>
<input type="text" id="txt">