[nodejs] read and write a file



        const fs = require("fs")

        try {
            // read from local folder
            const localPDF = fs.readFileSync('PDFs/myFile.pdf')

            //write back to local folder
            fs.writeFileSync('PDFs/writtenBack.pdf', localPDF )

        } catch (err) {

Converting to Base64

        try {
            // read from local folder
            const localPDF = fs.readFileSync('PDFs/myFile.pdf')
            const localBase64 = localPDF.toString('base64')

            //write back to local folder
            fs.writeFileSync(`PDFs/writtenBack.pdf`, localBase64, {encoding: 'base64'})

        } catch (err) {

Reading and writing using streams with pipe

        //read and write local file
        var reader = fs.createReadStream("PDFs/myFile.pdf")
        var writer = fs.createWriteStream('PDFs/writtenBack.pdf');

[nodejs] APIs and Microservices Projects

These are my notes while doing the course APIs and Microservices on https://www.freecodecamp.org. I highly recommend it if you prefer to try things directly rather than watching videos.

Timestamp Microservice


app.get("/api/timestamp/", (req, res) => {
  res.json({ unix: Date.now(), utc: Date() });

app.get("/api/timestamp/:date?", (req, res) => {

  //utc date?
  let date = new Date(req.params.date)
  if (date != "Invalid Date") {
   res.json({unix: date.getTime(), utc: date.toUTCString()});

  //unix timestamp?
  const dateInt = parseInt(req.params.date);
  date = new Date(dateInt).toUTCString();
  if (date != "Invalid Date") {
    res.json({unix: dateInt, utc: date});
  //invalid input
  res.json({ error: date });

Request Header Parser Microservice



var useragent = require('express-useragent');
var cookieParser = require('cookie-parser');
var requestLanguage = require('express-request-language');

// stuff...

  languages: ['en-US', 'zh-CN'],
  cookie: {
    name: 'language',
    options: { maxAge: 24*3600*1000 },
    url: '/languages/{language}'

app.get("/api/whoami", (req, res) => {
  res.json({"ipaddress": req.ip,
            "language": req.language,
            "software": req.useragent.source });

URL Shortener Microservice


const express = require('express');
const cors = require('cors');
const app = express();
const bodyParser = require('body-parser');
const dns = require('dns');

// Basic Configuration
const port = process.env.PORT || 3000;


app.use('/public', express.static(`${process.cwd()}/public`));

app.get('/', function(req, res) {
  res.sendFile(process.cwd() + '/views/index.html');

app.use(bodyParser.urlencoded({extended: false}));

let urls = [];

app.post("/api/shorturl/new", function(req, res) {
  const getHostnameFromRegex = (url) => {
  // run against regex
  const matches = url.match(/^https?\:\/\/([^\/?#]+)(?:[\/?#]|$)/i);
  // extract hostname (will be null if no match is found)
  return matches && matches[1];

  hostname = getHostnameFromRegex(req.body.url);
  console.log("Hostname: " + hostname);

  // if no hostname found, return here
  if (!hostname) res.json({ error: 'invalid url' });

  // check if url is valid
  dns.lookup(hostname, (error, addresses) => {

    if (!error) {
       let newUrl = { original_url : req.body.url, short_url : urls.length + 1};
    } else {
      res.json({ error: 'invalid url' });



app.get('/api/shorturl/:num', function(req, res) {

  for (let i = 0; i < urls.length; i++) {
    if (urls[i].short_url == req.params.num) {


app.listen(port, function() {
  console.log(`Listening on port ${port}`);

Exercise Tracker


const express = require('express')
const app = express()
const cors = require('cors')
const bodyParser = require('body-parser');
const mongoose = require('mongoose');

app.get('/', (req, res) => {
    res.sendFile(__dirname + '/views/index.html')

const listener = app.listen(process.env.PORT || 3000, () => {
    console.log('Your app is listening on port ' + listener.address().port)

app.use(bodyParser.urlencoded({ extended: false }));

//DB connect
mongoose.connect(process.env.MONGO_URI, { useNewUrlParser: true, useUnifiedTopology: true });

const { Schema } = mongoose;

//User Schema
const userSchema = new Schema({
    username: { type: String, required: true },
const User = mongoose.model("User", userSchema);

//Exercise Schema
const exerciseSchema = new Schema({
    userId: Schema.Types.ObjectId,
    description: { type: String, required: true },
    duration: { type: Number, required: true },
    date: { type: Date, default: Date.now }
const Exercise = mongoose.model("Exercise", exerciseSchema);

//POST user to DB
app.post("/api/exercise/new-user", (req, res) => {

    let user = new User({ username: req.body.username });

    user.save((err, data) => {
        //console.log("created User: " + data);
        if (err) return console.error(err);
        res.json({ username: data.username, _id: data._id });


//GET all users from DB
app.get("/api/exercise/users", (req, res) => {
    User.find((err, usersFound) => {
        if (err) return console.error(err);
        //console.error("users found: " + usersFound);

//POST exercise form data
app.post("/api/exercise/add", (req, res) => {

    let exercise = new Exercise({
        userId: req.body.userId,
        description: req.body.description,
        duration: req.body.duration,
        date: req.body.date ? req.body.date : Date.now()

    exercise.save((err, data) => {
        //console.log("created exercise: " + data);
        if (err) return console.error(err);
        User.findById(exercise.userId, (err, userFound) => {
            if (err) return console.error(err);
            //console.log("userFound " + userFound.username); 
                _id: data.userId,
                username: userFound.username,
                date: data.date.toDateString(),
                duration: data.duration,
                description: data.description

//GET exercise log
app.get("/api/exercise/log", (req, res) => {

    let userId = req.query.userId;
    let limit = Number(req.query.limit);

    //create query filter
    let filter = {};
    filter.userId = userId;

    if (req.query.from && req.query.to) {
        let fromDate = new Date(req.query.from);
        let toDate = new Date(req.query.to);
        filter.date = { $gte: fromDate, $lte: toDate };

    console.log("Filter " + JSON.stringify(filter));

    const queryExercises = (done) => {
            .exec((err, exercices) => {
                if (err) return console.error(err);

    const paseExercises = (exercices) => {
        let logArray = [];

        for (let i = 0; i < exercices.length; i++) {
            var obj = exercices[i];
                description: obj.description,
                duration: obj.duration,
                date: obj.date.toDateString()

        User.findById(userId, (err, userFound) => {
            if (err) return console.error(err);
            let logger = {
                _id: userId,
                username: userFound.username,
                count: logArray.length,
                log: logArray

    //Execute Query


File Metadata Microservice



var express = require('express');
var cors = require('cors');
var multer  = require('multer')
var upload = multer({ dest: 'uploads/' });

var app = express();

app.use('/public', express.static(process.cwd() + '/public'));

app.get('/', function (req, res) {
    res.sendFile(process.cwd() + '/views/index.html');

const port = process.env.PORT || 3000;
app.listen(port, function () {
  console.log('Your app is listening on port ' + port)

app.post('/api/fileanalyse', upload.single('upfile'), (req, res, next) => {
  res.json({ name: req.file.originalname, type: req.file.mimetype, size: req.file.size  });

[nodejs] MongoDB and Mongoose Challenges

These are my notes while doing the course APIs and Microservices on https://www.freecodecamp.org. I highly recommend it if you prefer to try things directly rather than watching videos.

MongoDB is a database that stores data records (documents) for use by an application. Mongo is a non-relational, “NoSQL” database. This means Mongo stores all associated data within one record, instead of storing it across many preset tables as in a SQL database.
Mongo’s use of JSON as its document storage structure makes it a logical choice when learning backend JavaScript. Accessing documents and their properties is like accessing objects in JavaScript.

Mongoose.js is an npm module for Node.js that allows you to write objects for Mongo as you would in JavaScript.

MongoDB Atlas is a MongoDB Database-as-a-Service platform.

Install and Set Up Mongoose

Add mongodb and mongoose to the project’s package.json.

    "dependencies": {
        "body-parser": "^1.15.2",
        "dotenv": "^8.2.0",
        "express": "^4.12.4",
        "mongodb": "^3.6.4",
        "mongoose": "^5.11.15"

Store your MongoDB Atlas database URI in a private .env file as MONGO_URI. Replace user and password.


Connect to the database using the following syntax:

const mongoose = require('mongoose');
mongoose.connect(process.env.MONGO_URI, { useNewUrlParser: true, useUnifiedTopology: true });

Create a Model

Everything in Mongoose starts with a Schema. Each schema maps to a MongoDB collection and defines the shape of the documents within that collection.

const { Schema } = mongoose;

const personSchema = new Schema({
  name: { type: String, required: true },
  age: Number,
  favoriteFoods: [String]

const Person = mongoose.model("Person", personSchema);

Create and Save a Record of a Model

The done() function is a callback that tells us that we can proceed after completing an asynchronous operation such as inserting, searching, updating, or deleting. It’s following the Node convention, and should be called as done(null, data) on success, or done(err) on error.

const createAndSavePerson = (done) => {

  let max = new Person({name: "Max", age: 31, favoriteFoods: ["Pasta"]});

  max.save((err, data) => {
    if (err) return console.error(err);
    done(null, data)


Create Many Records with model.create()

var arrayOfPeople = [
    {name: "Max", age: 31, favoriteFoods: ["Pasta"]},
    {name: "Toni", age: 21, favoriteFoods: ["Pizza"]},
    {name: "Paul", age: 34, favoriteFoods: ["Bolo", "Penne"]}

const createManyPeople = (arrayOfPeople, done) => {
  Person.create(arrayOfPeople, (err, people) => {
    if (err) return console.error(err);
    done(null, people);

Use model.find() to Search Your Database

Model.find() accepts a query document (a JSON object) as the first argument, then a callback. It returns an array of matches.

const findPeopleByName = (personName, done) => {
  Person.find({name: personName}, (err, personFound) => {
    if (err) return console.error(err);
    done(null, personFound);

Use model.findOne() to Return a Single Matching Document from Your Database

Model.findOne() behaves like Model.find(), but it returns only one document (not an array), even if there are multiple items.

const findOneByFood = (food, done) => {
  Person.findOne({favoriteFoods: food}, (err, personFound) => {
    if (err) return console.error(err);
    done(null, personFound);

Use model.findById() to Search Your Database By _id

When saving a document, MongoDB automatically adds the field _id, and set it to a unique alphanumeric key.

const findPersonById = (personId, done) => {
  Person.findById({_id: personId}, (err, personFound) => {
    if (err) return console.error(err);
    done(null, personFound);

Perform Classic Updates by Running Find, Edit, then Save

const findEditThenSave = (personId, done) => {
  const foodToAdd = 'hamburger';

  Person.findById(personId, (err, person) => {
    if(err) return console.log(err); 
    person.save((err, updatedPerson) => {
      if(err) return console.log(err);
      done(null, updatedPerson)

Perform New Updates on a Document Using model.findOneAndUpdate()

Use the function parameter personName as the search key. Set the person’s age to 20.
Note: You should return the updated document. To do that, you need to pass the options document { new: true } as the 3rd argument to findOneAndUpdate(). By default, these methods return the unmodified object.

const findAndUpdate = (personName, done) => {
  const ageToSet = 20;

  Person.findOneAndUpdate({name: personName}, {age: ageToSet}, { new: true }, (err, updatedDoc) => {
    if (err) return console.error(err);
    done(null, updatedDoc)

Delete One Document Using model.findByIdAndRemove()

const removeById = (personId, done) => {

  Person.findByIdAndRemove(personId, (err, personDeleted) => {
    if (err) return console.error(err);
    done(null, personDeleted)

Delete Many Documents with model.remove()

const removeManyPeople = (done) => {
  const nameToRemove = "Mary";

  Person.remove({name: nameToRemove}, (err, personsDeleted) => {
    if (err) return console.error(err);
    done(null, personsDeleted)

Chain Search Query Helpers to Narrow Search Results

const queryChain = (done) => {
  const foodToSearch = "burrito";

  Person.find({favoriteFoods: foodToSearch})
  .sort({name: 1}) //sort bei name
  .limit(2) //only 2 results
  .select({age: 0})  //hide age
  .exec((err, twoPersonFound) => {
    if (err) return console.error(err);
    done(null, twoPersonFound)

[nodejs] Basic Node and Express

These are my notes while doing the course APIs and Microservices on https://www.freecodecamp.org. I highly recommend it if you prefer to try things directly rather than watching videos.

Node.js is a JavaScript runtime that allows developers to write backend (server-side) programs in JavaScript. Node.js comes with a handful of built-in modules (small, independent programs) that help facilitate this purpose. Some of the core modules include:

  • HTTP: a module that acts as a server
  • File System: a module that reads and modifies files
  • Path: a module for working with directory and file paths
  • Assertion Testing: a module that checks code against prescribed constraints

Express (not included by default) runs between the server created by Node.js and the frontend pages of a web application. Also handles the app’s routing.


Start a Working Express Server

Let’s serve our first string! In Express, routes takes the following structure: app.METHOD(PATH, HANDLER). METHOD is an http method in lowercase. PATH is a relative path on the server. HANDLER is a function that Express calls when the route is matched.

app.get("/", (req, res) => {
  res.send("Hello Express");

Serve an HTML File

You can respond to requests with a file using the res.sendFile(path) method. This method needs an absolute file path. Use the Node global variable __dirname to calculate the path.
Send the /views/index.html file as a response to GET requests to the / path.

let absolutePath = __dirname + "/views/index.html";

app.get("/", (req, res) => {

Serve Static Assets

Using express middleware to serve static files (stylesheets, scripts, images): app.use(path, middlewareFunction)

let staticFilesPath = __dirname + "/public";

app.use("/", express.static(staticFilesPath));

Serve JSON on a Specific Route

A REST (REpresentational State Transfer) API allows data exchange in a simple way, without the need for clients to know any detail about the server.

let dataJson = {"message": "Hello json"};

app.get("/json", (req, res) => {

Use the .env File

The .env file is a hidden shell file that is used to pass environment variables to your application. Accessible from the app as process.env.VAR_NAME. Add variables to .env with this syntax: VAR_NAME=value

let dataJson = {"message": "Hello json"};

app.get("/json", (req, res) => {
 if (process.env.MESSAGE_STYLE === "uppercase") {
   dataJson.message = dataJson.message.toUpperCase();


Implement a Root-Level Request Logger Middleware

For every request, it should log to the console a string taking the following format: method path - ip. An example would look like this: GET /json - ::ffff:

app.use(function middleware(req, res, next) {
  console.log(req.method + " " + req.path + " - " + req.ip);

Chain Middleware to Create a Time Server

(req, res, next) => {
  req.time = new Date().toString();
(req, res) => {
  res.json({time: req.time})

Get Route Parameter Input from the Client

route_path: ‘/:word/echo’
actual_request_URL: ‘/myString/echo’
req.params: {word: ‘myString’}

app.get("/:word/echo", (req, res) => {
  res.json({"echo": req.params.word});

Get Query Parameter Input from the Client

route_path: ‘/name’
actual_request_URL: ‘/name?first=firstname&last=lastname’
req.query: {first: ‘firstname’, last: ‘lastname’}

app.get("/name", (req, res) => {
  res.json({name: `${req.query.first} ${req.query.last}`})

Use body-parser to Parse POST Requests

POST is the default method used to send client data with HTML forms. In REST convention, POST is used to send data to create new items in the database (a new user, or a new blog post).
In these kind of requests, the data doesn’t appear in the URL, it is hidden in the request body. The body is a part of the HTTP request, also called the payload.
Add "body-parser": "^1.15.2", in your package.json as dependencie to parse the body data.

var bodyParser = require('body-parser');
app.use(bodyParser.urlencoded({extended: false}));

Get Data from POST Requests

Mount a POST handler at the path /name.

app.post("/name", function(req, res) {
  res.json({name: `${req.body.first} ${req.body.last}`})

[nodejs] Managing Packages with NPM

These are my notes while doing the course APIs and Microservices on https://www.freecodecamp.org. I highly recommend it if you prefer to try things directly rather than watching videos.

The Node Package Manager (npm) is a command-line tool to share and control modules (or packages) of JavaScript code written for use with Node.js.

When starting a new project, npm generates a package.json file. This file lists the package dependencies for your project. Since npm packages are regularly updated, the package.json file allows you to set specific version numbers for each dependency. This ensures that updates to a package don’t break your project.

npm saves packages in a folder named node_modules. These packages can be installed in two ways:

  1. globally in a root node_modules folder, accessible by all projects.
  2. locally within a project’s own node_modules folder, accessible only to that project.

The package.json file is the center of any Node.js project or npm package. It stores information about your project, similar to how the <head> section of an HTML document describes the content of a webpage. It consists of a single JSON object where information is stored in key-value pairs.


  "name": "fcc-learn-npm-package-json", // your project name
  "author": "Max Mustermann",
  "description": "A project that does something awesome",
  "keywords": [ "descriptive", "related", "words", "freecodecamp" ],
  "license": "MIT", // inform users of what they are allowed to do with your project
  "version": "1.2.0", // describes the current version of your project
  "dependencies": {
    "package-name": "MAJOR.MINOR.PATCH", // Semantic Versioning
    "express": "^4.14.0", 
    "moment": "~2.10.2" // handy library for working with time and dates.

PATCHes are bug fixes and MINORs add new features but neither of them break what worked before. Finally, MAJORs add changes that won’t work with earlier versions.

To allow an npm dependency to update to the latest PATCH version, you can prefix the dependency’s version with the tilde (~) character.
The caret (^) will allow both MINOR updates and PATCHes.

[OpenUI5] SAP Fiori elements add-on for OpenUI5 using an OData V4 service

Recently I found this blog post about the new SAP Fiori elements add-on for OpenUI5.
It includes a little exercise to try it out for yourself. I wrote down all steps I had to make on my Linux Mint 20 installation.
These two links also helped me a lot.

Prerequisites (Node.js, Visual Studio Code, SAP Fiori tools, Git)

curl -sL https://deb.nodesource.com/setup_15.x | sudo -E bash -
sudo apt-get install -y nodejs
node --version
npm -v 

Change npm’s default directory to prevent permission errors.

mkdir ~/.npm-global
npm config set prefix '~/.npm-global'
mkdir ~/.npm-global/lib
#add the following line to your .bashrc or .profile or .zshrc
export PATH=~/.npm-global/bin:$PATH

Step 1: Provide an OData V4 service

git clone https://github.com/sap-samples/cloud-cap-samples remote-odata-service
cd remote-odata-service
npm i 
npm i -g @sap/cds-dk
cds watch fiori

Step 2: Generate a SAP Fiori elements List Report Object Page (LROP) app with Fiori tools

1. Open VSC, press Ctrl + P and search for > Fiori: Open Application Generator

2. Choose SAP Fiori elements application
In my case there was no default generator, so first I had to install it.

npm install -g @sap/generator-fiori-elements@latest

This can also be done directly in VSC.

3. Select List Report Object Page
4. Select Connect to an OData Service as Data source and enter as URL http://localhost:4004/browse
5. Choose Books as the Main entity and texts as Navigation entity
6. Complete the mandatory information module name (e.g. bookshop) and Project folder path for storing your app. Of course, you can also fill in the optional information.

Step 3: Make changes in package.json and ui5.yaml required for using OpenUI5


	"name": "fiorielements_openui5",
	"version": "0.0.1",
	"private": true,
	"sapux": true,
	"description": "A Fiori application.",
	"keywords": [
	"main": "webapp/index.html",
	"scripts": {
		"start": "fiori run --open index.html",
		"start-local": "fiori run --config ./ui5-local.yaml --open index.html",
		"build": "ui5 build -a --clean-dest --include-task=generateManifestBundle generateCachebusterInfo",
		"deploy": "fiori add deploy-config"
	"devDependencies": {
		"@sap/ux-specification": "latest",
		"@sap/ux-ui5-tooling": "1",
		"@ui5/cli": "2.5.0",
		"@ui5/fs": "2.0.1",
		"@ui5/logger": "2.0.0"
	"ui5": {
		"dependencies": [
	"dependencies": {
		"@sap/open.fe": "1.85.0"


specVersion: '2.2'
  name: 'fiorielements_openui5'
type: application
  name: OpenUI5  
  version: "1.85.0"  
  - name: sap.m  
  - name: sap.ui.core  
  - name: sap.uxap
  - name: themelib_sap_fiori_3
  - name: fiori-tools-proxy
    afterMiddleware: compression
      ignoreCertError: false # If set to true, certificate errors will be ignored. E.g. self-signed certificates will be accepted
      - path: /browse
        url: http://localhost:4004
  - name: fiori-tools-appreload
    afterMiddleware: compression
     port: 35729
     path: webapp

Step 4: Run the V4 application

cd ~/projects/fiorielements_openui5
npm i
npm start

Now http://localhost:8080/index.html should be opened in your browser.
“Note: Clicking on the Go button in List Report application might request  user and password. Please enter user alice, no password.”
Finally I got my list items.

[SAPUI5] Deploying the ui5 sample app on debian

I’m deploying the openui5-sample-app to an Linux Container running Debian Buster. First update the packages and install nodejs.

apt update && apt upgrade -y
apt install curl -y
curl -sL https://deb.nodesource.com/setup_12.x | bash -
apt install nodejs -y
nodejs --version

Install PM2 (process manager to manage Node.js applications) and the UI5 Tooling

npm install pm2 -g
npm install --global @ui5/cli

Now clone the openui5-sample-app and build it

apt install git
git clone https://github.com/SAP/openui5-sample-app.git
cd openui5-sample-app/
ui5 build -a
cd ..

Run your project on port 8000. With “startup” it will automatically create a systemd script.

pm2 serve openui5-sample-app/dist/ 8000
pm2 startup
pm2 save
systemctl start pm2-root
systemctl status pm2-root

[SAPUI5] local ui5 development

1. Install node.js

2. Install UI5 Tooling

npm install --global @ui5/cli

3. Install Easy UI5 Generator, create a project and run it on your localhost

npm install -g yo generator-easy-ui5
yo easy-ui5
cd <your project name> 
npm start

4. Set up a Github project and do your initial push

git add .
git commit -m "Initial commit"
git remote add origin https://github.com/user/myUI5App.git 
git push origin master

5. Install your favorite Editor, e.g. Visual Studio Code or Atom, and open your project to edit it