How do you load CSS and JS files dynamically

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);
}