JSFiddle - React, Tailwind, and code Playground

HTML

<form method="post" action="" enctype="multipart/form-data" id="myform" onsubmit="return checkForm(this)";>
    <input type="file" name="filename" />
    <input type="submit">
</form>

JavaScript

function checkForm(form){
    // process fieds
    return checkNextFunction(form);
}

function checkNextFunction(form){
     form.action = 'myurl.php';
     return true;
}