Angular and Chosen Plugin

Question

I used Chosen plugin in angular this is the snippet of the code

<select ng-model="vendor_value" ng-options="vendor.text for vendor in vendors" ui-jq="chosen" ui-options="{width: 300px}"></select>

then this will rendered in the browser

<select ng-model="category_value" ng-options="category.text for category in categories" style="border-color: red; display: none;" ui-jq="chosen" ui-options="{width: '300px', no_results_text: 'Press enter to add ', placeholder_text_single: '' }" class="ng-pristine ng-untouched ng-valid">
    <option value="?" selected="selected" label=""></option>
    <option value="0" label="Games">Games</option>
    <option value="1" label="Baby">Baby</option>
    <option value="2" label="Shoes">Shoes</option>
</select>
<div class="chosen-container chosen-container-single" style="width: 300px;" title="">
    <a class="chosen-single chosen-default" tabindex="-1"> <----- I want to insert a class after form is submitted in the angular controller
        <span>Select an Option</span>
    </a>
    <div class="chosen-drop">
        <div class="chosen-search">
            <input type="text" autocomplete="off">
        </div>
        <ul class="chosen-results"></ul>
    </div>
</div>

In this line

<a class="chosen-single chosen-default" tabindex="-1">

I want to insert a class after form is submitted. How can I insert class in a dynamically created html line by chosen plugin in angular controller?