Add CSS or JS on the fly

add-css-vanilla.js

function loadCss(url) {
  var link = document.createElement("link");
  link.type = "text/css";
  link.rel = "stylesheet";
  link.href = url;
  document.getElementsByTagName("head")[0].appendChild(link);
}

add-css.js

function loadCssJquery(url) {
  $('body').append('<link href="'+url+'" type="text/css" rel="stylesheet" />');
}

add-js-vanilla.js

function loadJs(url) {
  var script = document.createElement('script');
  script.src = url;
  // script.onload = function () { /* do stuff on load */ };
  document.head.appendChild(script);
}

add-js.js

function loadJsJquery(url) { 
  $('body').append('<script src="'+url+'"></script>'); 
}

load-jquery.js

// Loads jQuery if not present
!window.jQuery && loadJs('https://code.jquery.com/jquery-latest.min.js');