How do I submit a “file” input without submit button using JavaScript?

yes, you can use the form.submit() function. Add an onchange listener on the file input and link it to the form.submit() function, like so:

<form action="upload.php" method="post" enctype="multipart/form-data">
<input type="file" onchange="this.form.submit()" name="myFile"/>
</form>