获取事件对象

<input type="text" id="a1" value="111"/>
<input type="text" id="a2" value="222"/>  

<script type="text/javascript">
 log(document.getElementById("a1"));
 document.getElementById("a1").onclick=function(a){
  var event=arguments[0]||window.event;
  log(event);
  var element=event.target||event.srcElement;
  log(element.value);
 };

 console.log(document.getElementById("a2"));
 function fn_test1(a){
  log(a.value);
 }
 document.getElementById("a2").setAttribute("onclick",fn_test1);

 function log(sMsg) {
 typeof console=='undefined'?alert(sMsg):console.log(sMsg);
 }
  </script>