Single page apps in Express js - simple setup

I have been traversing the web for good tutorials on single page apps in Express.js. I have found a lot of different tutorials, and also some scaffolded projects. None of them seems easy to understand for me (they don't provide understanding of fundamentals), and therefore I allowed myself to start with a clean sheet.

I want the server side and client side to be completely decoupled. Therefore I want to serve a static web page with images and css script files and everything I need, and I want the backend to be a REST API. This is not hard:

var express = require("express");
var app = express();

app.use("/", express.static(__dirname + "/public"));

app.get("/api", function(req,res) {
res.send("Test")
})

var port = process.env.PORT || 8080;

app.listen(port);
console.log("Server up on port " + port);

Here I have the beginning structure. One simply serves the "public" directory statically, and all routes to the api on their own. This allows all subfolders of the public/ folders such as for instance public/images to be served as well. index.html is served if you only input server:8080/ and directory listing does not show.

In case of collisions the static files will be served instead of the route. For instance:

app.get("/images/test.gif", function(req,res) {
res.send("Test")
});

...when the file public/images/test.gif exists - the image will be served and not the route.