<html>
    <head>
    <script type="text/javascript">
        var t1=document.getElementById("txt1");
        function isFocus(){
            if(document.activeElement.id=='txt2'){
                alert('txt2获得焦点');
            }
            else{
                alert('txt2未获得焦点');
            }
        }
    </script>
    </head>
    <input id="txt1" type="text" value="aaaaa" onblur="isFocus()">
    <input id="txt2" type="text" value="bbbbb">
    <input id="txt3" type="text" value="cccc">
    </html>