JSFiddle - React, Tailwind, and code Playground

HTML

<form name="upload-form" id="upload-form" action="upload-information.php" enctype="multipart/form-data" method="post">

    <input type="file" name="dealers_csv" id="dealers_csv" required="required" data-message="Please attach the mcust.csv file.">

    <button type=\"submit\" name=\"Submit\" id=\"Submit\" class=\"csbutton-color upload-button\" style=\"margin-right:10px;\" >Submit files</button>

</form>

JavaScript

$(document).ready(function() {
    $("input#dealers_csv").on("change", function() {
        var dealers = $("input#dealers_png");
        var arrfilepath = dealers.val().split("\\");
        var filename = arrfilepath[arrfilepath.length - 1];
        alert(filename);
        if (filename != "mcust.csv") {
            alert("Wrong file!");
            dealers.val('');
        }
    });
});