用prototype.js怎樣寫圖片被單擊的事件？
<img id= "arrow " src= "select_arrow.gif " width= "15 " height= "18 " />
怎樣用prototype.js擴展的類或事件寫：
當$( "arrow ")被單擊時執行自定義函數a()？
[解决办法]
<script language= "javascript ">
Event.observe($( 'arrow '), 'click ', function(event) {
alert( 'a ');
});
</script>
