Question: ![enter image description here](https://i.stack.imgur.com/1rmh7.png)

I am trying to check if a user has logged in using `firebase.auth().onAuthStateChanged()`. When I run the code, the application does not load/render any pages.

Answer: 
Without further tweaks, you could do

```php
<form action="index" method="post">
    <?=
    DateTimePicker::widget([
        'name'          => 'datetime_10',
        'value'         => Yii::$app->request->post('datetime_10', null),
        'options'       => [
            'placeholder'  => 'Start Date Time',
            'autocomplete' => 'off',
            'required'     => true,
        ],
        'convertFormat' => false,
        'pluginOptions' => [
            'format'         => 'yyyy-mm-dd hh:i:ss',
            //'startDate' => '01-Mar-2014 12:00 AM',
            'todayHighlight' => true,
            'autoclose'      => true,
        ]
    ]);
    ?>
    <?=
    DateTimePicker::widget([
        'name'          => 'datetime_11',
        'value'         => Yii::$app->request->post('datetime_11', null),
        'options'       => [
            'placeholder'  => 'End Date Time',
            'autocomplete' => 'off',
            'required'     => true,
        ],
        'convertFormat' => false,
        'pluginOptions' => [
            'format'         => 'yyyy-mm-dd hh:i:ss',
            //'startDate' => '01-Mar-2014 12:00 AM',
            'todayHighlight' => true,
            'autoclose'      => true,
        ]
    ]);
    ?>
</form>

```

But this is not reliable. If you are gathering data throughout multiple pages, you should really consider storage/persistence, at least session & save to database after all the forms are completed, or skip session and go directly with in-memory data, a database etc.
You should assigne a value realted to your nodel->field and assigne/reassigne the value you need after (or before ) subimit 

```
<?=
    DateTimePicker::widget([
        'name' => 'datetime_10',
        'value' => $yourModel->yourField, // <------ this 
        'options' => [
                'placeholder' => 'Start Date Time',
                'autocomplete' => 'off',
            'required' =>true,
                ],
        'convertFormat' => false,
        'pluginOptions' => [
            'format' => 'yyyy-mm-dd hh:i:ss',
            //'startDate' => '01-Mar-2014 12:00 AM',
            'todayHighlight' => true,
            'autoclose' => true,
        ]
    ]);
 ?>

```