How to get the value of checkbox in Jquery

I have a HTML element:

<a style='text-decoration:none;' id='$innerdata[0]' class='cat' href='#'>&nbsp;&nbsp;&nbsp;&nbsp;<input type='checkbox' name='vehicle' value='Bike'>&nbsp;$innerdata[1]</a>

I am trying to get the value of checkbox.

$('body').on('click', '.cat', function() 
{
    $topcat = $(this);
    alert ($topcat.closest().find('[type=checkbox]').val());

}

But alert is printing undefined.

How to get the value of checkbox ??