only load custom.js if present

server/scripts/custom.sample.js

@@ -2,8 +2,7 @@
 // it is intended to allow for customizations that do not get published back to the git repo
 // for example, changing the logo
 
-// start running after all content is loaded
-document.addEventListener('DOMContentLoaded', () => {
+const customTask = () => {
 	// get all of the logo images
 	const logos = document.querySelectorAll('.logo img');
 	// loop through each logo
@@ -11,4 +10,16 @@ document.addEventListener('DOMContentLoaded', () => {
 		// change the source
 		elem.src = 'my-custom-logo.gif';
 	});
+};
+
+// start running after all content is loaded, or immediately if page content is already loaded
+if (document.readyState === 'loading') {
+	// Loading hasn't finished yet
+	document.addEventListener('DOMContentLoaded', customTask);
+} else {
+	// `DOMContentLoaded` has already fired
+	customTask();
+}
+document.addEventListener('DOMContentLoaded', () => {
+
 });