how do you unselect all items from a listbox using jquery

jQuery is designed to work with multiple elements at the same time:

$(listboxSelector).find("option").attr("selected", false);

$('#myListbox option').attr('selected',false);

The shortest way is this method:

$("#myListBox").val([]);

This sets the value to an empty array, meaning select no values. .val() takes an array in the case of a <select multiple> element. Note that $("select").val('');​​​​​​​ also works here :)