JSFiddle - React, Tailwind, and code Playground

HTML

<input id="btn" class="wpsc-buy-now-button wpsc-buy-now-button-64" type="image" name="submit" border="0" src="https://www.paypal.com/en_US/i/btn/btn_buynow_LG.gif" alt="PayPal - The safer, easier way to pay online" />

JavaScript

$(document).ready(function () {
    var $allClasses = $("[name='submit']").attr('class').split(' ');
    for(var i=0; i < $allClasses.length; i++)
    {
        // Check $allClasses[i] here.
        alert($allClasses[i]);
    }
});