ヘッダ部分
<SCRIPT LANGUAGE="JavaScript">
function getNumberA() {
document.forms[0].A.value = Math.floor(Math.random()*10)
timerID = setTimeout("getNumberA()",300)
}
</SCRIPT>
ボディ部分
<BODY onLoad="getNumberA()">
...
<FORM>
<INPUT TYPE="text" NAME="A" SIZE="1" onClick="clearTimeout(timerID)">
<INPUT TYPE="button" NAME="STOP" VALUE="STOP" onClick="clearTimeout(timerID)">
<INPUT TYPE="button" NAME="GO" VALUE="GO" onClick="getNumberA()">
</FORM>