Question

I have a function that adds a new unordered list item. I’d like to set one of the element’s values in the newly created list item to a value that is based on a value in the list item just above the new one.

For instance, if I have something like:

<form id="form" action="">

<ul id="list1" class="listing">

    <li id="input1" class="item">

        <input id="descr1" class="descr" type="text" value="" name="descr1" />
        <input id="group1" class="group" type="text" value="" name="group1" />
        <input id="order1" class="order_field" type="text" value="4" name="order1" />
        <input id="row1" class="checkbox" type="checkbox" value="1" name="select_row1" />

    </li>

    <li id="input2" class="item">

        <input id="descr2" class="descr" type="text" value="" name="descr2" />
        <input id="group2" class="group" type="text" value="" name="group2" />
        <input id="order2" class="order_field" type="text" value="5" name="order2" />
        <input id="row2" class="checkbox" type="checkbox" value="2" name="select_row2" />

    </li>

</ul>

If I run the function that creates a new list item, I want the value in #order2 to be incremented by 1 and then the new list item (that will now have #order3) will be set to 6. For example, after I have created the new list item it would look like this:

    <li id="input3" class="item">

        <input id="descr3" class="descr" type="text" value="" name="descr3" />
        <input id="group3" class="group" type="text" value="" name="group3" />
        <input id="order3" class="order_field" type="text" value="6" name="order3" />
        <input id="row3" class="checkbox" type="checkbox" value="3" name="select_row3" />

    </li>

I need to find a way to get to the last list item and get the value for the class .order_field and then use that value (+1) when I create the new list item. My issue is I’m not sure how to put together the selector for getting to the last list item’s .order_field value.

I hope that makes sense.

Thanks,
Shawn

Answer 1

It’s simply:

var value = $('#list1 li:last .order_field').val();

You also have to convert the value to a number, which you can do using parseInt or unary +:

var newValue = parseInt(value, 10) + 1;
// or
var newValue = +value + 1;