Tried to comply a bit with CesiumJS coding.

.editorconfig: copied from CesiumJS project.
Reindented according to EditorConfig.
Converted quotes into double quotes.

.editorconfig

@@ -0,0 +1,15 @@
+# http://editorconfig.org
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.md]
+trim_trailing_whitespace = false
+
+[*.glsl]
+indent_size = 4

app.js

@@ -1,16 +1,16 @@
-const Express = require('express');
-const Morgan = require('morgan');
+const Express = require("express");
+const Morgan = require("morgan");
 
 const PORT = 8001;
 
 const app = Express();
 
-app.use(Morgan('common'));
+app.use(Morgan("common"));
 app.use(Express.urlencoded({ extended: true }));
 
-app.use('/', Express.static(__dirname + '/htdocs'));
-app.use('/src', Express.static(__dirname + '/src'));
-app.use('/cesium', Express.static(__dirname + '/node_modules/cesium/Build/CesiumUnminified'));
-app.get('/', (req, res) => { res.redirect('index.html'); });
+app.use("/", Express.static(__dirname + "/htdocs"));
+app.use("/src", Express.static(__dirname + "/src"));
+app.use("/cesium", Express.static(__dirname + "/node_modules/cesium/Build/CesiumUnminified"));
+app.get("/", (req, res) => { res.redirect("index.html"); });
 
 app.listen(PORT);