JSFiddle - React, Tailwind, and code Playground

HTML

<form action="upload.php" enctype="multipart/form-data" method="POST" id="uploadform">
    <input id="openFile" name="img" type="file" />
</form>

JavaScript

$(document).ready(function () {
    $('#uploadform').on('change', function (evt) {
        console.log($(this)[0].size);
    });
});