How to get the least previous element filtering it by class?

I want to get the previous element that is closest to the .me element filtering it by a .a class.This script returns me undefined..Why it's returning me undefined and how do I fix this?

    <p class="a" id="a1">Hello Again</p>
    <div class="a" id="a2">And Again</div>
    <p  id="a3">And Again</p>
    <p class="me">And Again</p>
</div>
<script>

  alert($(".me").prev("p.a").attr("i开发者_如何学God"));

 </script>

The prev()^[docs] method only looks at the immediate sibling.

Use the prevAll()^[docs] method instead to consider all previous siblings.

$(".me").prevAll("p.a").attr("id")

The attr()^[docs] method will give the ID of the first matched element, which is the nearest.

If you want to be more explicit in selecting the nearest one, use the first()^[docs] method or the eq()^[docs] method.

$(".me").prevAll("p.a").first().attr("id")

$(".me").prevAll("p.a").eq( 0 ).attr("id")