Chosen, onload
HTML
<link rel="stylesheet" href="http://harvesthq.github.com/chosen/chosen/chosen.css">
<script src="http://harvesthq.github.com/chosen/chosen/chosen.jquery.js"></script>
<div>
<p>Single Select Box</p>
<select data-placeholder="Choose a Country..." class="chzn-select" style="width:350px;" id="favCities1">
<option value="Chennai">Chennai</option>
<option value="Dharmapuri">Dharmapuri</option>
<option value="Tiruchirappalli">Tiruchirappalli</option>
<option value="Thanjavur">Thanjavur</option>
<option value="Bangalore">Bangalore</option>
</select>
</div>
<div>
<p>Multiple Select Box</p>
<select data-placeholder="Choose a Country..." class="chzn-select" multiple style="width:350px;" tabindex="4" id="favCities">
<option value="Chennai">Chennai</option>
<option value="Dharmapuri">Dharmapuri</option>
<option value="Tiruchirappalli">Tiruchirappalli</option>
<option value="Thanjavur">Thanjavur</option>
<option value="Bangalore">Bangalore</option>
</select>
</div>
JavaScript
$(".chzn-seltect").chosen();
// AFTER AJAX REQUEST AND RESPONSE
var city = "Thanjavur";
var value = $("#favCities1 option:contains("+city+")").attr('selected', 'selected');
$(".chzn-select").val(city);
$(".chzn-select").trigger("liszt:updated");