Loading JS API dynamically

gistfile1.js

window.ControlPanelJSLoaded = function() { EcwidCheckout.init({/* something */}); };

var script = document.createElement('SCRIPT');
script.src = "https://checkout.ecwid.com/controlpanel-api.js";
script.charset = "utf-8";
script.setAttribute("type", "text/javascript");
script.onerror = function() { alert('Could not load script'); };
document.body.appendChild(script);