How to convert unordered list into nicely styled <select> dropdown using jquery?

$(function() {
    $('ul.selectdropdown').each(function() {
        var $select = $('<select />');

        $(this).find('a').each(function() {
            var $option = $('<option />');
            $option.attr('value', $(this).attr('href')).html($(this).html());
            $select.append($option);
        });

        $(this).replaceWith($select);
    });
});

EDIT

As with any jQuery code you want to run on page load, you have to wrap it inside $(document).ready(function() { ... }); block, or inside it's shorter version $(function() { ... });. I updated the function to show this.

EDIT

There was a bug in my code also, tried to take href from the li element.

$('ul.selectdropdown').each(function() {
    var select = $(document.createElement('select')).insertBefore($(this).hide());
    $('>li a', this).each(function() {
        var a = $(this).click(function() {
            if ($(this).attr('target')==='_blank') {
                window.open(this.href);
            }
            else {
                window.location.href = this.href;
            }
        }),
        option = $(document.createElement('option')).appendTo(select).val(this.href).html($(this).html()).click(function() {
            a.click();
        });
    });
});

In reply to your last comment, I modified it a little bit but haven't tested it. Let me know.

$('ul.selectdropdown').each(function() {
    var list = $(this), select = $(document.createElement('select')).insertBefore($(this).hide());

    $('>li a', this).each(function() {
        var target = $(this).attr('target'),
        option = $(document.createElement('option'))
            .appendTo(select)
            .val(this.href)
            .html($(this).html())
            .click(function(){
                if(target==='_blank') {
                    window.open($(this).val());
                }
                else {
                    window.location.href = $(this).val();
                }
            });
    });
    list.remove();
});