Save an image file in folder using jquery in YII2

Question

I have an update form where i also have preview option. My form is as below:

<div class="whyyour-form">

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

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

        <?= $form->field($model, 'image')->fileInput();?>
        <div class="myimage"><?php if(isset($model->image) && !$model->isNewRecord) {
            echo Html::img(\yii\helpers\Url::to($baseUrl.'/uploads/'.$model->image),['class' => 'image','width'=>200]);}?>
        </div>
        <?= $form->field($model, 'content')->textarea(['rows' => 10]) ?>

        <div class="form-group">
            <?= Html::submitButton($model->isNewRecord ? 'Save' : 'Save', ['class' => $model->isNewRecord ? 'btn mybtn' : 'btn mybtn']) ?>
             <?= Html::button('Preview',['id' => 'preview','class' => 'btn mybtn']);  ?>
        </div>

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

    </div>

On click of preview, I'm using Jquery to get the entered data. But when I have problem in getting the image and storing it into folder. My Jquery is as below:

<script>
    $( document ).ready(function() {

        $('#w0').on("click", function(event) {
            $form = $(this); //wrap this in jQuery
           id = $form.attr('action');
           lastChar = id.substr(id.length - 1); 
        });
        $('#preview').click(function() {

            var img =$("#whyyour-image")[0].files[0]; alert(img);

            var tagln = $("#whyyour-heading").val();
            tinyMCE.triggerSave();
            var des =$('#whyyour-content').val();alert(des);
            $.ajax({ 
                method: "POST",
                url:"<?php echo Yii::$app->urlManager->createAbsoluteUrl(['whyyour/preview'])?>",
                data: { id : lastChar, tag : tagln , description : des },
                success:function(data) {

                }
            });
        setTimeout(function() {
            validateForm();
        },1000);
        }); 
      function validateForm() {
                var url = 'http://localhost/yourcms/your/coststructure.php?id='+lastChar;
                     window.open(url);
             };
        });

</script>

All I receive when I get the image file is [Object-File]. how to save it in the folder using Jquery? My preview action is as below:

 public function actionPreview()
     {

       $model = $this->findModel($_REQUEST['id']);
        if($model){
            if(isset($_REQUEST['tag']) && !empty($_REQUEST['tag']) && isset($_REQUEST['description']) && !empty($_REQUEST['description']) ){
                $model->previewHeading= $_REQUEST['tag'];
                $model->previewContent = $_REQUEST['description'];
                if($model->save()) {
                      \Yii::$app->getSession()->setFlash('error', 'Product(s) Removed Successfully');
                } else {
                    return $this->render('update', [
                        'model' => $model,
                    ]);
                }
        } else {
            return $this->render('update', [
                'model' => $model,
            ]);
        }
     }
     }

Please Suggest. Any suggestions would be greatly appreciated.