jQuery set selected value in option box once the box has been loaded

I want to preset the value of a selectbox based on a hidden field. I need this after an error has been detected in a form to avoid the user having to set the value themselves again. I do this by setting the value of a hidden field server side. The problem I have seems to be that the select box isn't done yet at the time I try to set the selected value. Anyone know how to solve this (possibly in a very different way?)

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.js"></script>

<script type="text/javascript" charset="utf-8">
$(function(){
    // this functions loads the state select box with states if a country with states is selected
$("select#countries").change(function(){
  $.getJSON("/ajax/exhibition/getstates.php?idCountry="+$("select#countri开发者_C百科es").val(), function(j){
        var options = '';
        $.each(j, function(key, value){
            options += '<option value="' + key + '">' + value + '</option>';
        });
    $("select#state").html(options);
    });
});

});
$(document).ready(function(){
// preset the state select box on page ready
$('select#countries').change();

// set the selected value of the state select box
var foo = $('#statepreset').val();
$("select#state option[value="+foo+"]").attr('selected', 'selected');


});
</script>

I would suggest this approach:

function initSelect(defaultVal) {
    $("select#countries").change(function(){
        $.getJSON("/ajax/exhibition/getstates.php?idCountry="+$("select#countries").val(),     function(j){
            var options = '';
            $.each(j, function(key, value){
                options += '<option value="' + key + '">' + value + '</option>';
            });
            $("select#state").html(options);
            $("select#state option[value="+defaultVal+"]").attr('selected', 'selected');
        });
    }).change();
}


$(document).ready(function(){
    initSelect($('#statepreset').val());
});

The quick fix for this is to put the code that modifies the selection of the state, inside the callback (inside the getJSON callback)

$("select#countries").change(function(){
  $.getJSON("/ajax/exhibition/getstates.php?idCountry="+$("select#countries").val(), function(j){
        var options = '';
        $.each(j, function(key, value){
            options += '<option value="' + key + '">' + value + '</option>';
        });
    $("select#state").html(options);

    // set the selected value of the state select box
    var foo = $('#statepreset').val();
    $("select#state option[value="+foo+"]").attr('selected', 'selected');
    });
});

Remember that the callback you supply to the getJson call is only executed once the server replies.

You could add the preselect-code to the callback of the getJson

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.js"></script>

<script type="text/javascript" charset="utf-8">
$(function(){
    // this functions loads the state select box with states if a country with states is selected
$("select#countries").change(function(){
  $.getJSON("/ajax/exhibition/getstates.php?idCountry="+$("select#countries").val(), function(j){
        var options = '';
        $.each(j, function(key, value){
            options += '<option value="' + key + '">' + value + '</option>';
        });
        $("select#state").html(options);
        var foo = $('#statepreset').val();
        $("select#state option[value="+foo+"]").attr('selected', 'selected');
    });
});
});