问文件上传与php问题

EN

<form action="upload.php" method="post" enctype="multipart/form-data">
  <h1>Image-upload with preview</h1>
<div class="wrapper">
  <div class="box">
    <div class="js--image-preview"></div>
    <div class="upload-options">
      <label>
        <input type="file" class="image-upload" accept="image/*" name="fileToUpload" />
      </label>
    </div>
  </div>


if(isset($_POST["submit"])) {
$check = getimagesize($_FILES["fileToUpload"]["tmp_name"]);
if($check !== false) {
    echo "File is an image - " . $check["mime"] . ".";
    $uploadOk = 1;
} else {
    echo "File is not an image.";
    $uploadOk = 0;
}