Question

I’m trying to use jQuery and jQuery UI to drag a <ul> element horizontally located inside a <div>.

I’d like to get the coordinates of the buttons located inside the <li> elements to center them inside #the_parent, but the position I get changes every time I resize the browser window, how I can get a position relative to #the_parent?

<script type:"text/javascript">
    $(document).ready (function () {
        $(".button").click (function () {
            var offset = $(this).offset();
            alert (offset.left);
        });
    });
</script>
<style type="text/css">
    #dragme li { float:left; list-style:none; }
    #the_parent { width:100%; }
    .spacer { width:100px; }
    .button div { padding:5px; background-color:darkgrey; color:white; }
</style>
<!-- this is contained inside another div of width:600px and it's centered in the middle of the page -->
<div id="the_parent">
    <ul id="dragme">
        <li class="spacer"></li>
        <li id="btn_01" class="button">
            <div>click</div>
        </li>
        <li class="spacer"></li>
        <li id="btn_02" class="button">
            <div>click</div>
        </li>
        <li class="spacer"></li>
    </ul>
</div>

Answer 1

Looks like you want position() instead of offset(). From the jQuery docs:

offset(): Get the current coordinates of the first element in the set of matched elements, relative to the document.

position(): Get the current coordinates of the first element in the set of matched elements, relative to the offset parent.