Getting the value of an element in jQuery

My code is working good thanks to the help of members here. Now I have one last step / request. I have the following code that some may have seen before just in the last hour:

<script type="text/javascript">
    $(document).ready(function () {
        $("[id^=topic]").change(function () {
            var a = 'pk' + $(this).attr('id').replace('topic', '');
            var b = $(a).val()
            alert(b);
        });
    });
</script>

and then later on:

<td id='开发者_StackOverflowpk_1'>Cat</td>
<td id='pk_2'>Dog</td>   

This code picks out pk_1, pk_2 etc and places into the variable named "a". What I would like is not to get the value of the element pk_1. I tried some different ways of getting this and putting into "b". For example I added "#". None work. Sometimes the alert box shows the word "undefined" sometime nothing. Anyone have any suggestions?

Thank you all

Use .html() instead of .val():

...
var a = '#pk' + $(this).attr('id').replace('topic', '');
var b = $(a).html();
alert(b);

A couple of things

$(document).ready(function () {
    $("[id^=topic]").change(function () {
        var a = '#pk_' + $(this).attr('id').replace('topic', ''); //add # and _
        var b = $(a).html(); //use .html and not .val
        alert(b);
    });
})

This should work for you.

Since it's an id the selector should start with #. Prepend that to the selector. Also, a td element doesn't have a value, only input elements do. You probably want the inner text (or, perhaps, the html). If that's not working, then check that the ids are what you expect.

<script type="text/javascript">
    $(document).ready(function () {
        $("[id^=topic]").change(function () {
            var a = '#pk' + $(this).attr('id').replace('topic', '');
            var b = $(a).text()
            alert(a + ' has value ' + b);
        });
    });
</script>

Based on the fact that a very specific id, say id='topic_1' corresponds to exactly id='pk_1', I would say that you should be skipping over the whole replacing/manipulating id tags to find another.

Instead use the metadata plugin.

<input type=text id="topic1" class="topic {pk:#pk_1}"/>
<input type=text id="topic2" class="topic {pk:#pk_2}"/>

In script:

$(document).ready(function () {
    $(".topic").change(function () {
        alert($($(this).metadata().pk).html());
    }
}

metadata can be downloaded here:

http://plugins.jquery.com/project/metadata