下面是使用两种方法监视focus事件的示例：通过addEventListener函数和通过onfocus元素属性。

<script>
function onfocused(ev){
 document.getElementById('si').textContent=ev.target.id;
}
onload=function(){
 document.getElementById('einput').addEventListener('focus', onfocused, false);
 document.getElementById('ebutton').addEventListener('focus', onfocused, false);
};
</script>

<div id=si>?</div>
<br />
<br />
Via addEventListener:
<input id=einput type=button value="einput" />
<button id=ebutton>ebutton</button>
<br />
<br />
Via onfocus attribute:
<input id=iinput type=button value="iinput" onfocus="onfocused(event)" />
<button id=ibutton onfocus="onfocused(event)">ibutton</button>