jquery中常容易出错的checkbox的获得值

<meta charset="UTF-8"/>
<input type="checkbox" />点我
<script type="text/javascript" src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script type="text/javascript">
var input=$("input");
input.click(function(){
var val1=input.attr("checked");
var val2=input.is(":checked");
console.log(val1);//undefied
console.log(val2);//true or false
});

</script>