How to send data from a form using ajax and process it in the controller?

Question

Yii

On the index page, a GridView is rendered, the GridView renders models and actions to them (view, update, delete).
When you click on action update, a form opens with the ability to upload a file. I decided to do it differently. When you click on the action, a pop-up window is created (jquery confirm library), and the content (view update) is loaded in it. When you click on the save button in the view, everything works fine, but it looks ugly. Then I decided to remove the save button from the update view and add it to the popup. This is where things get interesting for me. The form data is sent and saved, but the image is not. I read something about form data in js. But something did not help or requires some special processing?

index

$('.action-update').click(function (e) {
        var title = $(this).data('title')
        var link = $(this).val()

        $.alert({
            title: title,
            content: 'url:' + link,
            columnClass: 'col-6',
            containerFluid: true,
            buttons: {
                saveButton: {
                    text: 'Сохранить',
                    btnClass: 'btn-green',
                    action: function () {
                        $.ajax({
                            url: link,
                            method: 'post',
                            data: $('form').serialize(),
                            success: function () {
                                console.log(1)
                            }
                        })
                    }
                },
                closeButton: {
                    text: 'Закрыть'
                }
            }
        })
    });

update

<?php

use yii\helpers\Html;
use yii\widgets\ActiveForm;

/* @var $this yii\web\View */
/* @var $model app\modules\admin\models\Specialist */
/* @var $form yii\widgets\ActiveForm */
?>

<div class="specialist-form">

    <?php $form = ActiveForm::begin(['options' => ['enctype' => 'multipart/form-data']]); ?>

    <?= $form->field($model, 'name')->textInput(['maxlength' => true]) ?>

    <?= $form->field($model, 'birthday')->textInput(['type' => 'date']) ?>

    <?= $form->field($model, 'dental_profile')->textInput(['maxlength' => true]) ?>

    <?= $form->field($model, 'basic_education')->textarea(['rows' => 6]) ?>

    <?= $form->field($model, 'additional_education')->textarea(['rows' => 6]) ?>

    <?= $form->field($model, 'experience')->textInput(['type' => 'date']) ?>

    <?= $form->field($model, 'about')->textarea(['rows' => 6]) ?>

    <?= $form->field($model, 'image')->fileInput() ?>

    <?= $form->field($model, 'active')->checkbox() ?>

    <div class="form-group">
        <?= Html::submitButton('Сохранить', ['class' => 'btn btn-success']) ?>
    </div>

    <?php ActiveForm::end(); ?>

</div>

controller action update

public function actionUpdate($id)
    {
        $this->layout = false;
        $model = $this->findModel($id);


        if ($model->load(Yii::$app->request->post()) && $model->save()) {
            if (UploadedFile::getInstance($model, 'image')) {
                $model->uploadImage();
            }

            return !$model->hasErrors() ? $this->asJson(['status' => true]) : $this->asJson(['status' => false, 'message' => $model->getErrors()]);
        }

        return $this->render('update', [
            'model' => $model,
        ]);
    }

Answer 1

1. yes, you really need to dig towards formdata i.e. .serialize() won't help here.
2. You can try this:
var formData = new FormData($('form')[0]);
and send formData already, I think there will be no problems here.