Select2 supports configuration of the bootstrap library version so that you can use this either with any Bootstrap version 3.x and above. For setting up the bootstrap version for your extension, you can configure the Select2::bsVersion property to one of the following.

• To use with bootstrap 3 library - you can set Select2::bsVersion property to any string starting with 3 (e.g. 3 or 3.3.7 or 3.x)

• To use with bootstrap 4 library - you can set Select2::bsVersion property to any string starting with 4 (e.g. 4 or 4.6.0 or 4.x)

• To use with bootstrap 5 library - you can set Select2::bsVersion property to any string starting with 5 (e.g. 5 or 5.1.0 or 5.x)

'params' => [
    'bsVersion' => '5.x', // this will set globally `bsVersion` to Bootstrap 5.x for all Krajee Extensions
    // other settings
    // 'adminEmail' => 'admin@example.com'
]

"yiisoft/yii2-bootstrap5": "@dev"

"yiisoft/yii2-bootstrap4": "@dev"

"yiisoft/yii2-bootstrap": "@dev"

The yii2-widget-select2 extension can be installed automatically or manually using one of these options:

$ php composer.phar require kartik-v/yii2-widget-select2 "dev-master"

"kartik-v/yii2-widget-select2": "dev-master"

• bsVersion: string | int, the bootstrap library version to be used for the extension. Refer the Bootstrap Info section for details and pre-requisites on setting this property.

  • To use with Bootstrap library - you can set this to any string starting with 3 (e.g. 3 or 3.3.7 or 4.x / 3.x)

  • To use with bootstrap 4 - you can set this to any string starting with 4 (e.g. 4 or 4.6.0 or 4.x)

  • To use with bootstrap 5 - you can set this to any string starting with 4 (e.g. 5 or 5.1.0 or 5.x)

• bsColCssPrefixes: array, the bootstrap grid column css prefixes mapping, the key is the bootstrap versions, and the value is an array containing the sizes and their corresponding grid column css prefixes. The class using this trait, must implement kartik\base\BootstrapInterface. If not set will default to:.

  [
     3 => [
        self::SIZE_X_SMALL => 'col-xs-',
        self::SIZE_SMALL => 'col-sm-',
        self::SIZE_MEDIUM => 'col-md-',
        self::SIZE_LARGE => 'col-lg-',
        self::SIZE_X_LARGE => 'col-lg-',
        self::SIZE_XX_LARGE => 'col-lg-',
     ],
     4 => [
        self::SIZE_X_SMALL => 'col-',
        self::SIZE_SMALL => 'col-sm-',
        self::SIZE_MEDIUM => 'col-md-',
        self::SIZE_LARGE => 'col-lg-',
        self::SIZE_X_LARGE => 'col-xl-',
        self::SIZE_XX_LARGE => 'col-xl-',
     ],
     5 => [
        self::SIZE_X_SMALL => 'col-',
        self::SIZE_SMALL => 'col-sm-',
        self::SIZE_MEDIUM => 'col-md-',
        self::SIZE_LARGE => 'col-lg-',
        self::SIZE_X_LARGE => 'col-xl-',
        self::SIZE_XX_LARGE => 'col-xxl-',
     ],
  ];
  

• data: array the select option data items. The array keys are option values, and the array values are the corresponding option labels. The array can also be nested (i.e. some array values are arrays too). For each sub-array, an option group will be generated whose label is the key associated with the sub-array. If you have a list of data models, you may convert them into the format described above using \yii\helpers\ArrayHelper::map().

• language: string the locale ID (e.g. fr, de) for the language to be used by the Select2 Widget. If this property not set, then the current application language will be used (i.e. Yii::$app->language). Note:With release v4.0 of the Select2 plugin, you can have multiple language Select2 widgets on the same page.

• theme: string the theme to be used for the Select2 widget. The following themes are available inbuilt with this widget:

  • Select2::THEME_KRAJEE_BS5 or 'krajee-bs5': This theme has been created specially by Krajee which matches bootstrap 4 styles and adds various enhancements to work with Yii2 Select2 widget. This will be set as the default theme, if bsVersion is set to 5.x.

  • Select2::THEME_KRAJEE_BS4 or 'krajee-bs4': This theme has been created specially by Krajee which matches bootstrap 4 styles and adds various enhancements to work with Yii2 Select2 widget. This will be set as the default theme, if bsVersion is set to 4.x.

  • Select2::THEME_KRAJEE or 'krajee': This theme has been created specially by Krajee which matches Bootstrap library styles and adds various enhancements to work with Yii2 Select2 widget. This will be set as the default theme, if bsVersion is set to 3.x.

  • Select2::THEME_MATERIAL or 'material': This theme is available since v2.1.5 and resembles the Google Material form input design.

  • Select2::THEME_DEFAULT or 'default': The default inbuilt Select2 theme.

  • Select2::THEME_CLASSIC or 'classic': The classic Select2 theme.

  • Select2::THEME_BOOTSTRAP or 'bootstrap': The Bootstrap library Select2 theme from github.com/fk/select2-bootstrap-theme.

  The theme property if not set, will automatically default to one of the following themes based on your bootstrap version:

  • Select2::THEME_KRAJEE_BS5 for Bootstrap 5.x.

  • Select2::THEME_KRAJEE_BS4 for Bootstrap 4.x.

  • Select2::THEME_KRAJEE for Bootstrap 3.x.

  You can define your own custom theme by setting this property and rendering the theme specific CSS on your page. Refer to the Select2 plugin documentation for details on creating themes.

• changeOnReset: bool whether to trigger change for Select2 input on form reset so the Select2 value is rightly reset. Defaults to true.

• hideSearch: bool whether to hide the search control and display a simple select. Defaults to false.

• maintainOrder: bool whether to maintain the order of tag / option selected for a multiple select. Defaults to true.

• showToggleAll: bool whether to show the toggle all button for selection all options in a multiple select. Defaults to true.

• toggleSettings: array, the toggle all button settings for selecting/unselecting all the options. This is applicable only for * multiple select. The following array key properties can be set:

  • selectLabel: string, the markup to be shown to select all records. Defaults to:

    • <i class="far fa-square"></i> Select all when Select2::bsVersion is set to 4.x or 5.x, OR

    • <i class="fas fa-unchecked"></i> Select all when Select2::bsVersion is set to 3.x.

  • unselectLabel: string, the markup to be shown to select all records. Defaults to:

    • <i class="far fa-check-square"></i> Unselect all when Select2::bsVersion is set to 4.x or 5.x, OR

    • <i class="fas fa-checked"></i> Unselect all when Select2::bsVersion is set to 3.x.

  • selectOptions: array, the HTML attributes for the container wrapping the select label. Defaults to []

  • unselectOptions: array, the HTML attributes for the container wrapping the unselect label. Defaults to []

  • options: array, the HTML attributes for the toggle button container. Defaults to ['class' => 's2-togall-button']

• initValueText: string, the text to displayed in Select2 widget for the initial value. This is useful and applicable when you are using the widget with ajax loaded data AND/OR you are not providing the data. Check the ajax usage section for an example.

• addon: array Adds an input group addon to the Select2 widget

  • prepend: array|string the prepend addon configuration. If set as a string, will be rendered as is. If set as an array, you can set the following keys:

    • content: string the prepend addon content

    • asButton: boolean whether the addon is a button or button group. Defaults to false.

  • append: array|string the append addon configuration. If set as a string, will be rendered as is. If set as an array, you can set the following keys:

    • content: string the append addon content

    • asButton: boolean whether the addon is a button or button group. Defaults to false.

  • groupOptions: array HTML options for the input group

  • contentBefore: string content placed before addon. This is not HTML encoded.

  • contentAfter: string content placed after addon. This is not HTML encoded.

• size: string size of the Select2 input, must be one of the size constants

  • LARGE or 'lg'

  • MEDIUM or 'md'

  • SMALL or 'sm'

• disabled: boolean whether the input widget is to be entirely disabled. Defaults to false.

• readonly: boolean whether the input widget is to be entirely readonly. Defaults to false.

• options: array the HTML attributes for the input tag. The following options are important:

  • multiple: boolean whether multiple or single item should be selected.

  • placeholder or prompt: string placeholder text for the select item. To set a placeholder, you must set one of placeholder or prompt.

• pluginLoading: boolean, whether to show a loading progress indicator in place of the input before plugin is completely loaded. Defaults to true.

• pluginOptions: array the Select2 JQuery plugin options. Refer the plugin options documentation for details. The widget automatically reacts to the following pluginOptions

  • data: If you set this within the pluginOptions, it will override the data set at widget level. A hidden text input will be rendered instead of a HTML select in this case.

  • ajax: If you wish to use ajax set this option instead of a separate ajax function.

  • tags: If you wish to display tags selection, use this option. Usually you must set this to true with the options['multiple'] enabled. However you can set this to true to add custom tags for both single and multiple select. When options['multiple'] is enabled, the tags work very similar to a multiple select input and reads and sends data as an array.

• pluginEvents: array the Select2 JQuery events. You must define events in event-name => event-function format. All events will be stacked in the sequence. Refer the plugin options documentation for details. For example:

  pluginEvents = [
      "change" => "function() { log('change'); }",
      "select2:opening" => "function() { log('select2:opening'); }",
      "select2:open" => "function() { log('open'); }",
      "select2:closing" => "function() { log('close'); }",
      "select2:close" => "function() { log('close'); }",
      "select2:selecting" => "function() { log('selecting'); }",
      "select2:select" => "function() { log('select'); }",
      "select2:unselecting" => "function() { log('unselecting'); }",
      "select2:unselect" => "function() { log('unselect'); }"
  ];
  

use kartik\select2\Select2

// Usage with ActiveForm and model
echo $form->field($model, 'state_1')->widget(Select2::classname(), [
    'data' => $data,
    'options' => ['placeholder' => 'Select a state ...'],
    'pluginOptions' => [
        'allowClear' => true
    ],
]);

// With a model and without ActiveForm
echo Select2::widget([
    'model' => $model,
    'attribute' => 'state_2',
    'data' => $data,
    'options' => ['placeholder' => 'Select a state ...'],
    'pluginOptions' => [
        'allowClear' => true
    ],
]);

// Without model and implementing a multiple select
echo '<label class="control-label">Provinces</label>';
echo Select2::widget([
    'name' => 'state_10',
    'data' => $data,
    'options' => [
        'placeholder' => 'Select provinces ...',
        'multiple' => true
    ],
]);

// A disabled select2 list input
echo '<label class="control-label">State</label>';
echo Select2::widget([
    'name' => 'state_11',
    'data' => $data,
    'disabled' => true
]);

use kartik\select2\Select2;
use kartik\popover\PopoverX;
use yii\bootstrap\Modal;

// Templating example of formatting each list element
$url = \Yii::$app->urlManager->baseUrl . '/images/flags/';
$format = <<< SCRIPT
function format(state) {
    if (!state.id) return state.text; // optgroup
    src = '$url' +  state.id.toLowerCase() + '.png'
    return '<img class="flag" src="' + src + '"/>' + state.text;
}
SCRIPT;
$escape = new JsExpression("function(m) { return m; }");
$this->registerJs($format, View::POS_HEAD);
echo '<label class="control-label">Provinces</label>';
echo Select2::widget([
    'name' => 'state_12',
    'data' => $data,
    'options' => ['placeholder' => 'Select a state ...'],
    'pluginOptions' => [
        'templateResult' => new JsExpression('format'),
        'templateSelection' => new JsExpression('format'),
        'escapeMarkup' => $escape,
        'allowClear' => true
    ],
]);

// Disable specific values for selection (for example disable third and fourth value)
echo Select2::widget([
    'name' => 'kv-type-01',
    'data' => [1 => "First", 2 => "Second", 3 => "Third", 4 => "Fourth", 5 => "Fifth"],
    'options' => [
        'placeholder' => 'Select a type ...',
        'options' => [
            3 => ['disabled' => true],
            4 => ['disabled' => true],
        ]
    ],
]);

// Using a select2 widget inside a modal dialog
Modal::begin([
    'options' => [
        'id' => 'kartik-modal',
        'tabindex' => false // important for Select2 to work properly
    ],
    'title' => 'Select2 Inside Modal',
    'toggleButton' => ['label' => 'Show Modal', 'class' => 'btn btn-lg btn-primary'],
]);
echo Select2::widget([
    'name' => 'state_40',
    'data' => $data,
    'options' => ['placeholder' => 'Select a state ...'],
    'pluginOptions' => [
        'allowClear' => true,
        'dropdownParent' => '#kartik-modal'
    ],
]);
Modal::end();

// Using a select2 widget inside a Krajee Yii2 PopoverX dialog
PopoverX::begin([
    'id' => 'kartik-popover',
    'header' => 'Select2 Inside PopoverX',
    'toggleButton' => ['label' => 'Show PopoverX', 'class' => 'btn btn-lg btn-primary'],
]);
echo Html::textInput('Address', '',  ['class' => 'form-control mb-3', 'placeholder' => 'Enter address...']);
echo Select2::widget([
    'name' => 'state_41',
    'data' => $data,
    'options' => ['placeholder' => 'Select a state ...', 'autocomplete' => 'new-password'],
    'pluginOptions' => [
        'allowClear' => true,
        'dropdownParent' => '#kartik-popover'
    ],
]);
echo Html::textInput('City', '',  ['class' => 'form-control mt-3', 'placeholder' => 'Enter city...']);
echo Html::textInput('Zip', '',  ['class' => 'form-control mt-3', 'placeholder' => 'Enter zity...']);
PopoverX::end();
PopoverX::end();
// Render a simple select by hiding the search control.
echo '<label class="control-label">Status</label>';
echo Select2::widget([
    'name' => 'status',
    'hideSearch' => true,
    'data' => [1 => 'Active', 2 => 'Inactive'],
    'options' => ['placeholder' => 'Select status...'],
    'pluginOptions' => [
        'allowClear' => true
    ],
]);

// Localization - set widget language to translate messages in your local language
// russian
echo Select2::widget([
    'name' => 'kv_lang_select1',
    'language' => 'ru',
    'data' => $data,
    'options' => ['placeholder' => 'Выберите состояние ...'],
    'pluginOptions' => [
        'allowClear' => true
    ],
]);
// french
echo Select2::widget([
    'name' => 'kv_lang_select2',
    'language' => 'fr',
    'data' => $data,
    'options' => ['placeholder' => 'Sélectionnez un état ...'],
    'pluginOptions' => [
        'allowClear' => true
    ],
]);

// Using themes
// Krajee Bootstrap 5.x / 4.x Theme
echo Select2::widget([
    'bsVersion' => '4.x',
    'name' => 'kv_theme_select1a',
    'data' => $data,
    'theme' => Select2::THEME_KRAJEE, // this is the default if theme is not set
    'options' => ['placeholder' => 'Select a state ...'],
    'pluginOptions' => [
        'allowClear' => true
    ],
]);

// Krajee Bootstrap 3.x Theme
echo Select2::widget([
    'bsVersion' => '3.x',
    'name' => 'kv_theme_select1b',
    'data' => $data,
    'theme' => Select2::THEME_KRAJEE, // this is the default if theme is not set
    'options' => ['placeholder' => 'Select a state ...'],
    'pluginOptions' => [
        'allowClear' => true
    ],
]);

<div class="row">
    <div class="col-sm-6">
       <label>Theme MATERIAL (Single)</label>
        <?php
        echo Select2::widget([
            'name' => 'kv_theme_material_1',
            'data' => $data,
            'theme' => Select2::THEME_MATERIAL,
            'options' => ['placeholder' => 'Select a state ...', 'autocomplete' => 'off'],
            'pluginOptions' => [
                'allowClear' => true
            ],
        ]);
        ?>
    </div>
    <div class="col-sm-6">
       <label>Theme MATERIAL (Multiple)</label>
        <?php
        echo Select2::widget([
            'name' => 'kv_theme_material_2',
            'data' => $data,
            'theme' => Select2::THEME_MATERIAL,
            'options' => ['placeholder' => 'Select a state ...', 'multiple' => true, 'autocomplete' => 'off'],
            'pluginOptions' => [
                'allowClear' => true
            ],
        ]);
        ?>
    </div>
</div>
<br>
<div class="row">
    <div class="col-sm-6">
       <label>Theme BOOTSTRAP (Single)</label>
        <?php
        echo Select2::widget([
            'name' => 'kv_theme_bootstrap_1',
            'data' => $data,
            'theme' => Select2::THEME_BOOTSTRAP,
            'options' => ['placeholder' => 'Select a state ...', 'autocomplete' => 'off'],
            'pluginOptions' => [
                'allowClear' => true
            ],
        ]);
        ?>
    </div>
    <div class="col-sm-6">
       <label>Theme BOOTSTRAP (Multiple)</label>
        <?php
        echo Select2::widget([
            'name' => 'kv_theme_bootstrap_2',
            'data' => $data,
            'theme' => Select2::THEME_BOOTSTRAP,
            'options' => ['placeholder' => 'Select a state ...', 'multiple' => true, 'autocomplete' => 'off'],
            'pluginOptions' => [
                'allowClear' => true
            ],
        ]);
        ?>
    </div>
</div>
<br>
<div class="row">
    <div class="col-sm-6">
       <label>Theme CLASSIC (Single)</label>
        <?php
        echo Select2::widget([
            'name' => 'kv_theme_classic_1',
            'data' => $data,
            'theme' => Select2::THEME_CLASSIC,
            'options' => ['placeholder' => 'Select a state ...', 'autocomplete' => 'off'],
            'pluginOptions' => [
                'allowClear' => true
            ],
        ]);
        ?>
    </div>
    <div class="col-sm-6">
       <label>Theme CLASSIC (Multiple)</label>
        <?php
        echo Select2::widget([
            'name' => 'kv_theme_classic_2',
            'data' => $data,
            'theme' => Select2::THEME_CLASSIC,
            'options' => ['placeholder' => 'Select a state ...', 'multiple' => true, 'autocomplete' => 'off'],
            'pluginOptions' => [
                'allowClear' => true
            ],
        ]);
        ?>
    </div>
</div>
<br>
<div class="row">
    <div class="col-sm-6">
       <label>Theme DEFAULT (Single)</label>
        <?php
        echo Select2::widget([
            'name' => 'kv_theme_default_1',
            'data' => $data,
            'theme' => Select2::THEME_DEFAULT,
            'options' => ['placeholder' => 'Select a state ...', 'autocomplete' => 'off'],
            'pluginOptions' => [
                'allowClear' => true
            ],
        ]);
        ?>
    </div>
    <div class="col-sm-6">
       <label>Theme DEFAULT (Multiple)</label>
        <?php
        echo Select2::widget([
            'name' => 'kv_theme_default_2',
            'data' => $data,
            'theme' => Select2::THEME_DEFAULT,
            'options' => ['placeholder' => 'Select a state ...', 'multiple' => true, 'autocomplete' => 'off'],
            'pluginOptions' => [
                'allowClear' => true
            ],
        ]);
        ?>
    </div>
</div>

use kartik\select2\Select2;
// Various Select2 Sizes
echo Select2::widget([
    'name' => 'kv-state-200',
    'data' => $data,
    'size' => Select2::SMALL,
    'options' => ['placeholder' => 'Select a state ...'],
    'pluginOptions' => [
        'allowClear' => true
    ],
]) .
Select2::widget([
    'name' => 'kv-state-210',
    'data' => $data,
    'size' => Select2::MEDIUM,
    'options' => ['placeholder' => 'Select a state ...'],
    'pluginOptions' => [
        'allowClear' => true
    ],
]) .
Select2::widget([
    'name' => 'kv-state-220',
    'data' => $data,
    'size' => Select2::LARGE,
    'options' => ['placeholder' => 'Select a state ...'],
    'pluginOptions' => [
        'allowClear' => true
    ],
]) .
Select2::widget([
    'name' => 'kv-state-230',
    'data' => $data,
    'size' => Select2::SMALL,
    'options' => ['placeholder' => 'Select a state ...', 'multiple' => true],
    'pluginOptions' => [
        'allowClear' => true
    ],
]) .
Select2::widget([
    'name' => 'kv-state-240',
    'data' => $data,
    'size' => Select2::MEDIUM,
    'options' => ['placeholder' => 'Select a state ...', 'multiple' => true],
    'pluginOptions' => [
        'allowClear' => true
    ],
]) .
Select2::widget([
    'name' => 'kv-state-250',
    'data' => $data,
    'size' => Select2::LARGE,
    'options' => ['placeholder' => 'Select a state ...', 'multiple' => true],
    'pluginOptions' => [
        'allowClear' => true
    ],
]);
$addon = [
    'prepend' => [
        'content' => '<i class="fas fa-globe"></i>'
    ],
    'append' => [
        'content' => Html::button('<i class="fas fa-map-marker-alt"></i>', [
                'class' => 'btn btn-primary',
                'title' => 'Mark on map',
                'data-toggle' => 'tooltip'
            ]),
        'asButton' => true
    ]
];
// FOR RTL orientation with addon, set 'options' => ['dir' => 'rtl'] in all of the above
// and set addon property to $addon

use kartik\select2\Select2;
$data = [
    "red" => "red",
    "green" => "green",
    "blue" => "blue",
    "orange" => "orange",
    "white" => "white",
    "black" => "black",
    "purple" => "purple",
    "cyan" => "cyan",
    "teal" => "teal"
];

// Tagging support Multiple
$model->colorTags =  ['red', 'green']; // initial value
echo $form->field($model, 'colorTags')->widget(Select2::classname(), [
    'data' => $data,
    'options' => ['placeholder' => 'Select a color ...', 'multiple' => true],
    'pluginOptions' => [
        'tags' => true,
        'tokenSeparators' => [',', ' '],
        'maximumInputLength' => 10
    ],
])->label('Tag Multiple');

// Tagging support Multiple (maintain the order of selection)
echo '<label class="control-label">Tag Multiple</label>';
echo Select2::widget([
    'name' => 'color_2',
    'value' => ['red', 'green'], // initial value
    'data' => $data,
    'maintainOrder' => true,
    'options' => ['placeholder' => 'Select a color ...', 'multiple' => true],
    'pluginOptions' => [
        'tags' => true,
        'maximumInputLength' => 10
    ],
]);

// Tagging support (Multiple) for an update scenario that maintains the order of 
// selected tags on initialization when the (maintain the order of selection)
echo '<label class="control-label">Tag Multiple</label>';
echo Select2::widget([
    'name' => 'color_2a',
    'value' => ['teal', 'green', 'red'], // initial value (will be ordered accordingly and pushed to the top)
    'data' => $data,
    'maintainOrder' => true,
    'options' => ['placeholder' => 'Select a color ...', 'multiple' => true],
    'pluginOptions' => [
        'tags' => true,
        'maximumInputLength' => 10
    ],
]);

// Tagging support Multiple (maintain the order of selection)
echo '<label class="control-label">Tag Multiple</label>';
echo Select2::widget([
    'name' => 'color_3',
    'value' => ['red', 'green'], // initial value
    'data' => $data,
    'maintainOrder' => true,
    'toggleAllSettings' => [
        'selectLabel' => '<i class="fas fa-check-circle"></i> Tag All',
        'unselectLabel' => '<i class="fas fa-times-circle"></i> Untag All',
        'selectOptions' => ['class' => 'text-success'],
        'unselectOptions' => ['class' => 'text-danger'],
    ],
    'options' => ['placeholder' => 'Select a color ...', 'multiple' => true],
    'pluginOptions' => [
        'tags' => true,
        'maximumInputLength' => 10
    ],
]);

// Tagging support Single
echo '<label class="control-label">Tag Single</label>';
echo Select2::widget([
    'name' => 'color_3',
    'value' => 'red', // initial value
    'data' => $data,
    'options' => ['placeholder' => 'Select a color ...'],
    'pluginOptions' => [
        'tags' => true,
        'tokenSeparators' => [',', ' '],
        'maximumInputLength' => 10
    ],
]);

/*******
 * View
 ******/

// The controller action that will render the list
$url = \yii\helpers\Url::to(['city-list']);

// The widget
use kartik\select2\Select2; // or kartik\select2\Select2
use yii\web\JsExpression;
use yii\helpers\ArrayHelper;
use common\models\City;

// Get the initial saved city data (note $model->city is an array of city ids)
$dataList = City::find()->andWhere(['id' => $model->city])->all();
$data = ArrayHelper::map($dataList, 'id', 'name');

echo $form->field($model, 'city')->widget(Select2::classname(), [
    'data' => $data,
    'options' => ['multiple'=>true, 'placeholder' => 'Search for a city ...'],
    'pluginOptions' => [
        'allowClear' => true,
        'minimumInputLength' => 3,
        'language' => [
            'errorLoading' => new JsExpression("function () { return 'Waiting for results...'; }"),
        ],
        'ajax' => [
            'url' => $url,
            'dataType' => 'json',
            'data' => new JsExpression('function(params) { return {q:params.term}; }')
        ],
        'escapeMarkup' => new JsExpression('function (markup) { return markup; }'),
        'templateResult' => new JsExpression('function(city) { return city.text; }'),
        'templateSelection' => new JsExpression('function (city) { return city.text; }'),
    ],
]);

/*************
 * Controller
 ************/
public function actionCityList($q = null, $id = null) {
    \Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
    $out = ['results' => ['id' => '', 'text' => '']];
    if (!is_null($q)) {
        $query = new Query;
        $query->select('id, name AS text')
            ->from('city')
            ->where(['like', 'name', $q])
            ->limit(20);
        $command = $query->createCommand();
        $data = $command->queryAll();
        $out['results'] = array_values($data);
    }
    elseif ($id > 0) {
        $out['results'] = ['id' => $id, 'text' => City::find($id)->name];
    }
    return $out;
}

$formatJs = <<< 'JS'
var formatRepo = function (repo) {
    if (repo.loading) {
        return repo.text;
    }
    var markup =
'<div class="row">' + 
    '<div class="col-sm-5">' +
        '<img src="' + repo.owner.avatar_url + '" class="img-rounded" style="width:30px" />' +
        '<b style="margin-left:5px">' + repo.full_name + '</b>' + 
    '</div>' +
    '<div class="col-sm-3"><i class="fa fa-code-fork"></i> ' + repo.forks_count + '</div>' +
    '<div class="col-sm-3"><i class="fa fa-star"></i> ' + repo.stargazers_count + '</div>' +
'</div>';
    if (repo.description) {
      markup += '<p>' + repo.description + '</p>';
    }
    return '<div style="overflow:hidden;">' + markup + '</div>';
};
var formatRepoSelection = function (repo) {
    return repo.full_name || repo.text;
}
JS;

// Register the formatting script
$this->registerJs($formatJs, View::POS_HEAD);

// script to parse the results into the format expected by Select2
$resultsJs = <<< JS
function (data, params) {
    params.page = params.page || 1;
    return {
        results: data.items,
        pagination: {
            more: (params.page * 30) < data.total_count
        }
    };
}
JS;
// render your widget
echo Select2::widget([
    'name' => 'kv-repo-template',
    'value' => '14719648',
    'initValueText' => 'kartik-v/yii2-widgets',
    'options' => ['placeholder' => 'Search for a repo ...'],
    'pluginOptions' => [
        'allowClear' => true,
        'minimumInputLength' => 1,
        'ajax' => [
            'url' => "https://api.github.com/search/repositories",
            'dataType' => 'json',
            'delay' => 250,
            'data' => new JsExpression('function(params) { return {q:params.term, page: params.page}; }'),
            'processResults' => new JsExpression($resultsJs),
            'cache' => true
        ],
        'escapeMarkup' => new JsExpression('function (markup) { return markup; }'),
        'templateResult' => new JsExpression('formatRepo'),
        'templateSelection' => new JsExpression('formatRepoSelection'),
    ],
]);

use kartik\select2\Select2;
use kartik\helpers\Html;

echo Select2::widget([
    'name' => 'state_200',
    'data' => $us_states,
    'size' => Select2::MEDIUM,
    'addon' => [
        'prepend' => [
            'content' => '<i class="fas fa-globe"></i>'
        ],
        'append' => [
            'content' => Html::button('<i class="fas fa-map-marker-alt"></i>', [
                'class' => 'btn btn-primary', 
                'title' => 'Mark on map', 
                'data-toggle' => 'tooltip'
            ]),
            'asButton' => true
        ]
    ]
]);