source: pro-violet-viettel/sourcecode/application/modules/frontend/views/user_infor.php

<form id="admin_update_user_form">


    <div class="col-xs-12"  style="margin: 5px;">
        <div class="form-group">
            <label for="form-field-first" class="col-sm-4 control-label no-padding-right">Họ và tên</label>
            <div class="col-sm-8">
                <input type="text" name="fullname" value="<?php echo @$user['fullname']; ?> " placeholder="Họ và tên" id="form-field-first" class="col-xs-12 col-sm-10">
            </div>
        </div>
    </div>



    <div class="col-xs-12"  style="margin: 5px;">
        <div class="form-group">
            <label for="form-field-username" class="col-sm-4 control-label no-padding-right">Đơn vị</label>
            <div class="col-sm-8">
                <input type="text" name="school" value="<?php echo @$user['school']; ?>" placeholder="Đơn vị" id="form-field-username" class="col-xs-12 col-sm-10">
            </div>
        </div>
    </div>

    <div class="col-xs-12" style="margin: 5px;">
        <div class="form-group">
            <label for="form-field-username" class="col-sm-4 control-label no-padding-right">Tỉnh / Thà nh phố</label>
            <div class="col-sm-8">
                <select name="province" id="form-field-province" class="form-field-province-user col-xs-12 col-sm-10">
                                        <option></option>
                    <?php foreach ($provinces as $key => $pro): ?>
                        <option value="<?php echo $key; ?>" <?php if ($user['province'] == $key) echo "selected"; ?>><?php echo $pro; ?></option>
                    <?php endforeach; ?>
                </select>
            </div>
        </div>
    </div>
        <div class="col-xs-12" style="margin: 5px;">
                <div class="form-group">
                        <label for="form-field-username" class="col-sm-4 control-label no-padding-right">Quận / Huyện</label>
                        <div class="col-sm-8">
                                <select name="district" id="form-field-district" class="form-field-district-user col-xs-12 col-sm-10">

                                </select>
                        </div>
                </div>
        </div>

    <input type="hidden" name="us_id" value="<?php echo $user['us_id'] ?>">
    <?php
    if (in_array("editUserInfo", $roles)) {
        ?><div class="col-xs-12" style="margin: 5px;">
            <div class="form-group">
                <input  class="btn btn-primary pull-right " type="button" value="Cập nhật" onclick="admin_update_user();"/>
            </div>
        </div>
        <?php
    }
    ?>
</form>
<script>
var district_id = "<?php echo $user['district']; ?>";
var province_id = "<?php echo $user['province']; ?>";

$(document).ready(function(){
        $(".form-field-province-user").change(function(){
                changeEventProvince(province_id);
        });
        if ($(".form-field-province-user").val() !== 'undefined'){
                checkSelectedDistrict(province_id);
        }
});

function changeEventProvince(provinceId){
        $(".form-field-district-user").html("");
        $.ajax({
        url: '/frontend/user/getDistrict/' + provinceId,
        type: 'POST',
        success: function (data, textStatus, jqXHR)
        {
            result = jQuery.parseJSON(data);
                        content = "<option></option>";
                        if (result != null){
                                for (var i in result){                  
                                        content = content + '<option value="' + result[i].district_id + '">'+ result[i].type + " "  + result[i].district_name + '</option>'
                                }
                        }
                        $(".form-field-district-user").html(content);
        }
    });
}

function checkSelectedDistrict(provinceId){
        $.ajax({
        url: '/frontend/user/getDistrict/' + provinceId,
        type: 'POST',
        success: function (data, textStatus, jqXHR)
        {
            result = jQuery.parseJSON(data);    
                        content = "<option></option>";
                        if (result != null){
                                for (var i in result){
                                        if (result[i].district_id === district_id){
                                                content = content + '<option value="' + result[i].district_id + '" selected >' + result[i].type + " " + result[i].district_name + '</option>';
                                        }else{
                                                content = content + '<option value="' + result[i].district_id + '">' + result[i].type + " "  + result[i].district_name + '</option>';
                                        }
                                }
                                
                        }
                        $(".form-field-district-user").html(content);
        }
    });
}
</script>