Solution 1 : Try this for JS. <form action=""> <label for="file">Select file:</label> <input type="file" name="file" accept="text/js"> </form> Info on accept https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/file#attr-accept Configuring server MIME types https://developer.mozilla.org/en-US/docs/Learn/Server-side/Configuring_server_MIME_types MIME types https://www.sitepoint.com/mime-types-complete-list/ Problem…

Solution 1 : You can get help from this doc. https://flask.palletsprojects.com/en/2.1.x/patterns/fileuploads/ Solution 2 : def allowed_file(filename): return '.' in filename and filename.rsplit('.', 1)[1].lower() in app.config['UPLOAD_EXTENSIONS'] pass the file name to…