You can create both link and script elements in the DOM and append them as child to head tag. Let's create a function to add script and style resources as below,
function loadAssets(filename, filetype) { if (filetype == "css") { // External CSS file var fileReference = document.createElement("link"); fileReference.setAttribute("rel", "stylesheet"); fileReference.setAttribute("type", "text/css"); fileReference.setAttribute("href", filename); } else if (filetype == "js") { // External JavaScript file var fileReference = document.createElement("script"); fileReference.setAttribute("type", "text/javascript"); fileReference.setAttribute("src", filename); } if (typeof fileReference != "undefined") document.getElementsByTagName("head")[0].appendChild(fileReference); }