How do I add options to a DropDownList using jQuery?

Without using any extra plugins,

var myOptions = {
    val1 : 'text1',
    val2 : 'text2'
};
var mySelect = $('#mySelect');
$.each(myOptions, function(val, text) {
    mySelect.append(
        $('<option></option>').val(val).html(text)
    );
});

If you had lots of options, or this code needed to be run very frequently, then you should look into using a DocumentFragment instead of modifying the DOM many times unnecessarily. For only a handful of options, I'd say it's not worth it though.

------------------------------- Added --------------------------------

DocumentFragment is good option for speed enhancement, but we cannot create option element using document.createElement('option') since IE6 and IE7 are not supporting it.

What we can do is, create a new select element and then append all options. Once loop is finished, append it to actual DOM object.

var myOptions = {
    val1 : 'text1',
    val2 : 'text2'
};
var _select = $('<select>');
$.each(myOptions, function(val, text) {
    _select.append(
            $('<option></option>').val(val).html(text)
        );
});
$('#mySelect').append(_select.html());

This way we'll modify DOM for only one time!

With the plugin: jQuery Selection Box. You can do this:

var myOptions = {
        "Value 1" : "Text 1",
        "Value 2" : "Text 2",
        "Value 3" : "Text 3"
    }
    $("#myselect2").addOption(myOptions, false); 

And also, use .prepend() to add the option to the start of the options list. http://api.jquery.com/prepend/

Lets think your response is "successData". This contains a list which you need to add as options in a dropdown menu.

success: function (successData) {
var sizeOfData = successData.length;
if (sizeOfData == 0) {
    //    NO DATA, throw an alert ...
    alert ("No Data Found");
} else {
    $.each(successData, function(val, text) {
        mySelect.append(
            $('<option></option>').val(val).html(text)
        );
    });
} }

This would work for you ....