Question:

I know one can get the value of the currently selected item like this:

var myListBoxItemText = $('#myListBox').val().toString();

But how do you change this value in the list box to something else?

Seeing your update in the comments, here's an updated answer. Just use the <a href="http://api.jquery.com/selected-selector/" rel="nofollow">:selected</a> selector to filter the options inside of your select element to get the selected option.

To change a select element's selected option's value property:

$('#myListBox option:selected').val('new value');

To change its display text:

$('#myListBox option:selected').text('new text');

<em><strong><a href="http://jsfiddle.net/ult_combo/NubSF/" rel="nofollow">JSFiddle</a></strong></em>

$("#myListBox").val("This is the new value");

Although, by 'listbox', I assume you mean a select element. In which case you'll have to add the property selected to one of the child option elements.

$('#myListBox').val(your_val);

Here your_val denotes the value attribute of <option>

Or you can also use

$('#myListBox')[0].selectedIndex = 1;

or

$('#myListBox').prop('selectedIndex', 1);

<strong><a href="http://jsfiddle.net/thecodeparadox/QStkd/175/" rel="nofollow">DEMO</a></strong>

<strong><a href="http://jsfiddle.net/thecodeparadox/QStkd/176/" rel="nofollow">DEMO 2</a></strong>