Q:

Angular2 Routing in conjunction to Express routing?

My angular2 app's routes don't work when accessed via URL... Express is rendering an error page instead.
So I have one route (/docs) which serves some static content and some other static resources, however, / is routed to an index.html which is managed by angular 2. So by opening the application root and then clicking various router links I can get to a route e.g. /tutorial/chapter/1. However, as that isn't a registered route in my express app, if I refresh the page I get a 404. 
I want to be able to type http://localhost:3000/tutorial/chapter/1 into my browser and get that page. How do I set express to route all undefined routes to angular, and let angular handle the 404?
Here is my app.js:
var app = express();

// html view engine setup
app.set('views', path.join(__dirname, '/ng2/views'));
app.engine('html', require('jade').renderFile);
app.set('view engine', 'html');

app.use(express.static('ng2/views'));
app.use(express.static('ng2/public'));

app.use('/node_modules', express.static(__dirname + '/node_modules'));    

// uncomment after placing your favicon in /public
app.use(favicon(path.join(__dirname, 'ng2/public', 'favicon.png')));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());

//all static assetes for hexo content

app.use('/docs', serveStatic('features/docs/public', { 'index': ['index.html', 'index.htm'] }));

app.use('/', routes);

// catch 404 and forward to error handler
app.use(function (req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

module.exports = app;

You can see the full repo here
Here is the routes middleware def:
var express = require('express');
var router = express.Router();

/* GET home page. */
router.get('/', function(req, res, next) {
  res.render('index', { title: 'Express' });
});

module.exports = router;

A:

Angular 2 assumes that independent of the request URL, the frontend will be returned. This assumption is based on a feature modern browsers implement called push state. You have 3 options if you want to support anything but the bleeding edge of browsers:

Recommended: Seperate the API server from the client.
If you put your client on example.org and your express backend on api.example.org you can just do what Angular assumes to be true. You can also deploy independently and the client can live on a static host or CDN. This will require that you setup CORS though.   
Catch-All Express Route
Make sure all your routes in Express differ from the ones you setup in NG2 and make a catch-all handler. Put something like this at the end of your routes/middleware but before the 404 handler!
app.use(function(req, res, next) {
  res.sendFile("index.html");
})

Use legacy browser-url-styles for the router.
You can make the NG2 router use hashes for routes. Check here.

A:

app.js
Since order is important and new code is inserted in multiple locations, the whole file is included. Look for comment started with // JS -
var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var serveStatic = require('serve-static')
var file = require('./features/prepareTutorial');
var routes = require('./ng2/routes/index');

var app = express();

// html view engine setup
app.set('views', path.join(__dirname, '/ng2/views'));
app.engine('html', require('jade').renderFile);
app.set('view engine', 'html');

app.use(express.static('ng2/views'));
app.use(express.static('ng2/public'));

app.use('/node_modules', express.static(__dirname + '/node_modules'));
app.use('/persist', express.static(__dirname + '/persist'));

// JS - Add /app
app.use('/app', express.static(__dirname + '/ng2/views/app'));

// I have to comment this line because it failed
//file.processTutorial(); //generate html rendered patches for tutorial steps
//file.genGit(); //generate git SHA
file.processChapters();

// uncomment after placing your favicon in /public
app.use(favicon(path.join(__dirname, 'ng2/public', 'favicon.png')));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());

//all static assetes for hexo content

app.use('/docs', serveStatic('features/docs/public', { 'index': ['index.html', 'index.htm'] }));
//app.use(subdomain('docs', express.static('docs/public')));
app.use('/script', serveStatic('features/docs/public/script'));
app.use('/style', serveStatic('features/docs/public/style'));
app.use('/images', serveStatic('features/docs/public/images'));
app.use('/diff', serveStatic('features/tutorial/diffs'));
app.use('/git', serveStatic('features/git'));
app.use('/chapter', serveStatic('ng2/views/app/tutorial/chapter/chapters'));
app.use('/img', serveStatic('features/docs/source/img'));

app.use('/config', serveStatic('ng2/config'));

app.use('/', routes);

// JS - /tutorial static
//app.use('/tutorial', express.static('ng2/views/app/tutorial'));
// JS - /tutorial/chapter/* send index file 
app.all(/^\/tutorial$/, (req, res) => {
  res.redirect('/tutorial/');
});
app.use('/tutorial/', (req, res) => {
  res.sendFile(__dirname + '/ng2/views/index.html');
});

// catch 404 and forward to error handler
app.use(function (req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

// error handlers

// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
  app.use(function (err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
      message: err.message,
      error: err
    });
  });
}

// production error handler
// no stacktraces leaked to user
app.use(function (err, req, res, next) {
  res.status(err.status || 500);
  res.render('error', {
    message: err.message,
    error: {}
  });
});

module.exports = app;

ng2/config/systemjs.config.js & ng2/public/config/systemjs.config.js
Use absolute path
This is the main issue. With relative path, the browser is requesting files at tutorial/chapter/2/app/*, tutorial/chapter/2/node_modules/*, etc, and the app break down completely.
// snip ...
var map = {
    'app':                        '/app', // 'dist',
    '@angular':                   '/node_modules/@angular',
    'angular2-in-memory-web-api': '/node_modules/angular2-in-memory-web-api',
    'rxjs':                       '/node_modules/rxjs'
  };
// snip ...

ng2/views/index.html
Use absolute path
This won't stop the page from loading but a mess.
// snip ...
<link rel="stylesheet" href="/stylesheets/style.css">
// snip ...

