Key Points

1. Nodejs fits web server, batch, script program requirements

References

Key Concepts

NVM - Node Version Manager

https://github.com/nvm-sh/nvm#installing-and-updating

nvm-sh_nvm_ Node Version Manager - POSIX-compliant bash script to manage multiple active node.js versions.pdf

set the NVM default version then always run

nvm use default 

can set this in the user profile script:  .bashrc in the Home directory

Node, NPM support install

uninstall globals before installing NVM to manage Node, NPM

https://docs.npmjs.com/cli/v6/commands/npm-uninstall/

to remove the NPM global package 

npm uninstall -g 

Use NVM command ( in user/.bashrc ) to install Node, NPM

https://bytearcher.com/articles/ways-to-get-the-latest-node.js-version-on-a-mac/

Ubuntu NVM install 

https://askubuntu.com/questions/426750/how-can-i-update-my-nodejs-to-the-latest-version

Uninstall Nodejs on MACOS

https://stackoverflow.com/questions/11177954/how-do-i-completely-uninstall-node-js-and-reinstall-from-beginning-mac-os-x

Options to Update Node.js

https://phoenixnap.com/kb/update-node-js-version

Use Node config module to manage environment variables

https://zetcode.com/javascript/nodeconfig/

Node-config tutorial shows how to create configuration files for Node applications with node-config module.

Node-config

Node-config creates configuration files for application deployments.

Node-config allows us to define a set of default parameters and extend them for different deployment environments (development, qa, staging, production, etc.).

The configuration files are located in the default config directory. The location can be overriden with the NODE_CONFIG_DIR environment variable. The NODE_ENV environment variable contains the name of our application's deployment environment; it is development by default.

Node config supports various configuration file formats, including JSON, YAML, properties, or XML. The default configuration file is default.json (or default.yaml, default.xml). If we use a production deployment, then the configuration is loaded from production.json.

Setting up Node-config

First, we install node-config.

$ node -v
v11.5.0

We use Node version 11.5.0.

$ npm init -y

We initiate a new Node application.

$ npm i config

We install node-config with nmp i config.

$ npm i js-yaml

In addition, we install js-yaml for YAML support.

Node-config example

The following example retrieves configuration data with config package.

{
    "app": {
        "port": 3000
    },
    "db": {
        "host": "localhost",
        "port": 27017,
        "name": "ydb"
    }
}

We have default.json in the config directory.

const config = require('config');

let appPort = config.get('app.port');
console.log(`Application port: ${appPort}`);

let dbHost = config.get('db.host');
console.log(`Database host: ${dbHost}`);

let dbPort = config.get('db.port');
console.log(`Database port: ${dbPort}`);

let dbName = config.get('db.name');
console.log(`Database name: ${dbName}`);

console.log('NODE_ENV: ' + config.util.getEnv('NODE_ENV'));

We load the config package and get the values with config.get() function. The default deployment type is specified in NODE_ENV.

$ node simple.js
Application port: 3000
Database host: localhost
Database port: 27017
Database name: ydb
NODE_ENV: development

This is the output.

Node-config example II

We change the configuration file to YAML and set a production deployment environment.

app:
  port: 3000

db: 
  host: localhost
  port: 27017
  name: ydb

This is default.yaml file.

app:
  port: 3300

db: 
  host: localhost
  port: 27017
  name: mydb

This is production.yaml file.

const config = require('config');

let appPort = config.get('app.port');
console.log(`Application port: ${appPort}`);
...

The simple.js file is the same.

$ node simple.js
Application port: 3000
Database host: localhost
Database port: 27017
Database name: ydb
NODE_ENV: development

This is the output for the default environment. The configuration is loaded from default.yaml.

$ set NODE_ENV=production
$ node simple.js
Application port: 3300
Database host: localhost
Database port: 27017
Database name: mydb
NODE_ENV: production

We change the NODE_ENV variable with the set command. (Use export on Linux.) Now the configuration data is loaded from production.yaml file.

In this tutorial, we have used node-config package to create configuration files for our Node.js application.

NPM config package to configure different runtime environments

https://www.npmjs.com/package/config

Node-config organizes hierarchical configurations for your app deployments.

It lets you define a set of default parameters, and extend them for different deployment environments (development, qa, staging, production, etc.).

Configurations are stored in configuration files within your application, and can be overridden and extended by environment variables, command line parameters, or external sources.

This gives your application a consistent configuration interface shared among a growing list of npm modules also using node-config.

Project Guidelines

• Simple - Get started fast
• Powerful - For multi-node enterprise deployment
• Flexible - Supporting multiple config file formats
• Lightweight - Small file and memory footprint
• Predictable - Well tested foundation for module and app developers

Quick Start

The following examples are in JSON format, but configurations can be in other file formats.

Install in your app directory, and edit the default config file.

$ npm install config
$ mkdir config
$ vi config/default.json

{
  // Customer module configs
  "Customer": {
    "dbConfig": {
      "host": "localhost",
      "port": 5984,
      "dbName": "customers"
    },
    "credit": {
      "initialLimit": 100,
      // Set low for development
      "initialDays": 1
    }
  }
}

Edit config overrides for production deployment:

 $ vi config/production.json

{
  "Customer": {
    "dbConfig": {
      "host": "prod-db-server"
    },
    "credit": {
      "initialDays": 30
    }
  }
}

Use configs in your code:

const config = require('config');
//...
const dbConfig = config.get('Customer.dbConfig');
db.connect(dbConfig, ...);

if (config.has('optionalFeature.detail')) {
  const detail = config.get('optionalFeature.detail');
  //...
}

config.get() will throw an exception for undefined keys to help catch typos and missing values. Use config.has() to test if a configuration value is defined.

Start your app server:

$ export NODE_ENV=production
$ node my-app.js

Running in this configuration, the port and dbName elements of dbConfig will come from the default.json file, and the host element will come from the production.json override file.

Edit Nodejs in VSCode Tutorial

https://code.visualstudio.com/docs/nodejs/nodejs-tutorial

Simple Nodejs Examples to run Server

https://stackabuse.com/how-to-start-a-node-server-examples-with-the-most-popular-frameworks/

Nodejs application frameworks 

https://softwareontheroad.com/nodejs-frameworks/

nodejs-app-frameworks-examples-The Best 10 Nodejs Frameworks for 2019

MANY Nodejs basic tips and tutorials

https://www.freecodecamp.org/news/search/?query=nodejs

https://flaviocopes.com/node-read-csv/

Node handook pdf

nodejs-servers-How to Start a Node Server Examples with the Most Popular Frameworks.pdf

nodejs-the-complete-guide-course-at-udemy-.pdf

https://www.freecodecamp.org/news/how-to-build-a-todo-app-with-react-typescript-nodejs-and-mongodb/

https://www.freecodecamp.org/news/create-a-professional-node-express/

https://www.freecodecamp.org/news/node-js-production-checklist/

https://www.freecodecamp.org/news/stripe-and-node-js-4-best-practices-and-examples/

Node.js debug

https://www.freecodecamp.org/news/watch-sockets-with-this-grunt-plugin/

https://www.freecodecamp.org/news/node-js-debugging/

Node AWS

https://www.freecodecamp.org/news/how-to-build-and-deploy-graphql-server-in-aws-lambda-using-nodejs-and-cloudformation/

https://www.freecodecamp.org/news/how-to-reuse-packages-with-aws-lambda-functions-using-amplify/

Nodejs Basics 

https://www.w3schools.com/nodejs/ref_modules.asp

includes crypto, 

CLI args - yargs option for parms

https://nodejs.org/en/knowledge/command-line/how-to-parse-command-line-arguments/

how yargs handles your arguments. Here's a quick reference:

• argv.$0 contains the name of the script file which is executed like: '$0': 'myapp.js'.
• argv._ is an array containing each element not attached to an option(or flag) these elements are referred as commands in yargs.
• Individual options(flags) become properties of argv, such as with argv.h and argv.time. Note that non-single-letter flags must be passed in as --flag like: node myapp.js --time.

A summary of elements used in the program:

• argv: This is the modified process.argv which we have configured with yargs.
• command(): This method is used to add commands, their description and options which are specific to these commands only, like in the above code lyr is the command and -y is lyr specific option: node myapp.js lyr -y 2016
• option(): This method is used to add global options(flags) which can be accessed by all commands or without any command.
• help(): This method is used to display a help dialogue when --help option is encountered which contains description of all the commands and options available.
• alias(): This method provides an alias name to an option, like in the above code both --help and -h triggers the help dialogue.

For more information on yargs and the many, many other things it can do for your command-line arguments, please visit http://yargs.js.org/docs/

Node.js CLI app with OAuth security

https://developer.okta.com/blog/2019/06/18/command-line-app-with-nodejs

node-cli-ex-oauth-developer.okta-Build a Command Line Application with Nodejs.pdf

Modules - builtin and custom 

https://www.w3schools.com/nodejs/nodejs_modules.asp

exports.myDateTime = function () {
  return Date();
};

Use the exports keyword to make properties and methods available outside the module file.

Save the code above in a file called "myfirstmodule.js

Include modules with require

var http = require('http');
var dt = require('./myfirstmodule');

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.write("The date and time are currently: " + dt.myDateTime());
  res.end();
}).listen(8080);

Http module to create a server

Need a header record for type 

Pass req, res variables to set request, get response

var http = require('http');
http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.write(req.url);
  res.end();
}).listen(8080);

fs File system module

https://www.w3schools.com/nodejs/nodejs_filesystem.asp

Create files

The File System module has methods for creating new files:

• fs.appendFile()
• fs.open()
• fs.writeFile()

Update files

The File System module has methods for updating files:

• fs.appendFile()
• fs.writeFile()

The fs.appendFile() method appends the specified content at the end of the specified file:

Delete a file

var fs = require('fs');

fs.unlink('mynewfile2.txt', function (err) {
  if (err) throw err;
  console.log('File deleted!');
})

Upload File Module - Formidable 

https://www.w3schools.com/nodejs/nodejs_uploadfiles.asp

Include the Formidable module to be able to parse the uploaded file once it reaches the server.

When the file is uploaded and parsed, it gets placed on a temporary folder on your computer.

Reading and Write file example 

Stackbase example - Nodejs read, write csv files

https://stackabuse.com/reading-and-writing-csv-files-in-nodejs-with-node-csv/

install the entire node-csv suite:

npm install node-csv

Read csv file with fileStream and Callback api

csv-parse package provides multiple approaches for parsing CSV files - using callbacks, a stream + callback as well as the Sync and Async API. We'll be covering the stream + callback API and the Sync API.

var fs = require('fs'); 
var parse = require('csv-parse');
var parser = parse({columns: true}, function (err, records) {
console.log(records);
});

fs.createReadStream(__dirname+'/chart-of-accounts.csv').pipe(parser);

, we create a parser which accepts an object literal, containing the options we'd like to set. The second argument is the callback function that's used to access the records - or just print them out, in our case.

Options to specify for the fs include:

• The delimiter option defaults to a comma ,. If the data from the file you’re trying to parse uses some other delimiter like a semi-colon ;, or a pipe |, you can specify that with this option.

• The cast option defaults to false and is used to indicate whether you want to cast the strings to their native data types. For example, a column that is made up of date fields can be cast into a Date.

• The columns option is to indicate whether you want to generate the record in the form of object literals. By default, this column is set to false and records are generated by the parser in the form of arrays. If set to true, the parser will infer the column name from the first line.

Read file using Sync API and promises

var fs = require('fs').promises;
var parse = require('csv-parse/lib/sync');
(async function () {
const fileContent = await fs.readFile(__dirname+'/chart-of-accounts.csv');
const records = parse(fileContent, {columns: true});
console.log(records)
})();

we're creating an async function, in which we retrieve the contents of the file by awaiting the response of the readFile() function.

Then, we can create a parser which takes in the file contents as the first argument and an object literal as the second. This object literal contains options for creating the parser (we've set columns to true). This parser is assigned to a constant variable and we simply print its contents out for brevity's sake:

Write file using csv-stringify

from the node-csv suite. Stringification just means that we'll convert some data (JSON in our example) into a string. This string is then written to a file, in CSV format.

The csv-stringify package also has a couple of API options, though, the Callback API offers a really simple way to stringify data, without the need to handle events like with the Stream API.

reading csv file with Stringifier

stringifier.on('readable', function(){
  let row;
  while(row = stringifier.read()){
    data.push(row)
  }
})

URL module 

https://www.w3schools.com/nodejs/nodejs_url.asp

Parse an address with the url.parse() method, and it will return a URL object with each part of the address as properties:

var url = require('url');
var adr = 'http://localhost:8080/default.htm?year=2017&month=february';
var q = url.parse(adr, true);

console.log(q.host); //returns 'localhost:8080'
console.log(q.pathname); //returns '/default.htm'
console.log(q.search); //returns '?year=2017&month=february'

var qdata = q.query; //returns an object: { year: 2017, month: 'february' }
console.log(qdata.month); //returns 'february'

NPM package manager installed with Node.js

https://www.w3schools.com/nodejs/nodejs_npm.asp

NPM is a package manager for Node.js packages, or modules if you like.

www.npmjs.com hosts thousands of free packages to download and use.

The NPM program is installed on your computer when you install Node.js

A package in Node.js contains all the files you need for a module.

Modules are JavaScript libraries you can include in your project.

npm install mypackage

Events module

https://www.w3schools.com/nodejs/nodejs_events.asp

you can create-, fire-, and listen for- your own events.

Similar to Java beans where events are built-in with create event, addListener, fireEvent

Objects in Node.js can fire events, like the readStream object fires events when opening and closing a file:

Readstream example on file open

var fs = require('fs');
var rs = fs.createReadStream('./demofile.txt');
rs.on('open', function () {
  console.log('The file is open');
});

Create eventEmitter

var events = require('events');
var eventEmitter = new events.EventEmitter();

Email module 

https://www.w3schools.com/nodejs/nodejs_email.asp

NestJS - framework for building efficient, scalable Node.js server-side applications.

https://docs.nestjs.com/

Flexible app context

https://docs.nestjs.com/application-context

There are several ways of mounting the Nest application. You can create either a web app, microservice or just a Nest application context. Nest context is a wrapper around the Nest container, which holds all instantiated classes. We can grab an existing instance from within any imported module directly using application object. Hence, you can take advantage of the Nest framework everywhere, including CRON jobs and even build a CLI on top of it.

Getting started#

In order to create a Nest application context, we use the following syntax:

async function bootstrap() {
  const app = await NestFactory.createApplicationContext(ApplicationModule);
  // application logic...
}
bootstrap();

Afterward, Nest allows you to pick any instance registered within Nest application. Let's imagine that we have a TasksService in the TasksModule. This class provides a set of usable methods, which we want to call from within CRON job.

const app = await NestFactory.create(ApplicationModule);
const tasksService = app.get(TasksService);

And that's it. To grab TasksService instance we had to use get() method. We didn't have to go through entire modules tree, the get() method act like a query that search for an instance in each registered module automatically. However, if you prefer a strict context checking, you can always switch to it using strict: true options object that has to be passed as the second argument of get() method. Then, you have to go through all modules to pick up a particular instance from the selected context.

Express request routing

Example from Piotr using a common sdk on FE, BE

const dmxSdkFactory = require('@dmx/npm-dmx-sdk');// it's important to create an sdk instance, both on BE and FE
const dmxSdk = sdkFactory({
  getLogger,
  senderMicroserviceName,
  environment,
});// a middleware in Koa or Express
app.use(injectDmxSdk(dmxSdk));// outside of requests like in data ingestion or running a migration or handling an AMQP event or on FE
dmxSdk.DMX.Payments().get({ path: '/payments/deals' });// when handling a request
ctx.dmxSdk.DMX.Payments().get({ path: '/payments/deals' });// when handling a call to an external service:
ctx.dmxSdk.Ext.Sendgrid().sendMail({ fromEmail, toEmail, subject, templateId });

Nodejs courses for MongoDB development

Connect to a MongoDB Database Using Node.js: https://bit.ly/3u7cvMB

MongoDB and Node.js Tutorial: https://bit.ly/3sOxX8M

Aggregation Framework with Node.js Tutorial: https://bit.ly/3sBbYCt

How to Use MongoDB Transactions in Node.js: https://bit.ly/31zopCE

Change Streams & Triggers with Node.js Tutorial: https://bit.ly/3m4kJlX

Mongoose and schema access to MongoDb

Populate on query result

’ll check the endpoint.
This should be setting sellingPrice as a priceSchema which is:

{
  dollars: Number,
  cents: Number (optional),
  currency: 'usd' (default)
}

Simple Web Sockets example

https://drive.google.com/file/d/1jdcAQrY3zLP3AiSu0DCSx0w2F38KjDmq/view

Conceptually, the WebSocket protocol is an extension to HTTP which allows clients to“upgrade” an HTTP connection with an additional bi-directional connection which remainsestablished, like this:

1. Client opens HTTP connection to server and asks for document
2. Server responds with an HTML document
3. HTTP connection is closed
4. JavaScript code in the HTML document opens another HTTP connection in which it asks the server to upgrade this connection to a WebSocket connection
5. A WebSocket connection between client and server is established and remains open forsending and receiving data in both directions

Technically, a WebSocket connection is simply a TCP connection on port 80, just like normalHTTP connections are - with the difference that client and server treat the connection in aspecial way.

Server code

index.js

var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);

app.get('/', function(req, res) {
    res.sendFile(__dirname + '/index.html');
});

io.on('connection', function(socket) {
    console.log('A new WebSocket connection has been established');
});

setInterval(function() {
  var stockprice = Math.floor(Math.random() * 1000);
  io.emit('stock price update', stockprice);
}, 2000);

http.listen(8000, function() {
    console.log('Listening on *:8000');
});

Client code

index.html

<!doctype html>
<html>
  <head>
    <title>Live stock price ticker</title>

    <script src="/socket.io/socket.io.js"></script>
    <script src="https://code.jquery.com/jquery-3.2.1.min.js"></script>

    <script>
      $(function () {
        var socket = io();

        socket.on('stock price update', function(stockprice) {
          $('#stockprice').text(stockprice);
        });

      });
    </script>

  </head>
  <body>
    Stock price: <span id="stockprice">no data yet</span>
  </body>
</html>

To build the example ...

after installing node and npm

mkdir wstest
cd wstest
node install   // creates the application in wstest
// in a text editor, create index.js 
// in a test editor, create index.html

To run example ....

Start node server

cd /blearn/js
node wstest\index.js

Start client web page

In firefox, enter the url for the server to load the HTML page

http://localhost:8000/

The page will be updated from the server with new stock prices periodically

Javascript ( ES17 ) Async Await Support

https://medium.com/javascript-in-plain-english/async-await-javascript-5038668ec6eb

await for function completion must be inside a function with async support as shown below

await is a new operator used to wait for a promise to resolve or reject. It can only be used inside an async function.

Promise.all returns an array with the resolved values once all the passed-in promises have resolved.

// test1.js  --- run with nodejs 
//
async function aGetRandomNbr() {
	return 111
};

async function doThis() {
var aNbr = await aGetRandomNbr();
console.log(`test1.js completed with value: ${aNbr} `);
};

doThis();

To run example ...

node test1.js 

Javascript promises support example

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all

Promise.all(iterable);
Promise.all waits for all fulfillments (or the first rejection).

Parameters

Section

iterable An iterable object such as an Array.

Return value

Section

• An already resolved Promise if the iterable passed is empty.
• An asynchronously resolved Promise if the iterable passed contains no promises. Note, Google Chrome 58 returns an already resolved promise in this case.
• A pending Promise in all other cases. This returned promise is then resolved/rejected asynchronously (as soon as the stack is empty) when all the promises in the given iterable have resolved, or if any of the promises reject. See the example about "Asynchronicity or synchronicity of Promise.all" below. Returned values will be in order of the Promises passed, regardless of completion order.

var promise1 = Promise.resolve(3);
var promise2 = 42;
var promise3 = new Promise(function(resolve, reject) {
  setTimeout(resolve, 100, 'foo');
});

Promise.all([promise1, promise2, promise3]).then(function(values) {
  console.log(values);
});
// expected output: Array [3, 42, "foo"]

create file PromiseTest.js with the code above

To run example

node PromiseTest.js 

output =

Nodejs read and write to MongoDB example 

/*
nt-mongo-atlas2.js

https://docs.mongodb.com/drivers/node/quick-start
https://docs.mongodb.com/drivers/node/
https://docs.mongodb.com/drivers/node/usage-examples
find by ObjectId ex
https://docs.mongodb.com/drivers/node/usage-examples/findOne
https://kb.objectrocket.com/mongo-db/nodejs-mongodb-find-by-id-686
https://docs.mongodb.com/drivers/node/usage-examples/updateOne
https://docs.mongodb.com/drivers/node/usage-examples/replaceOne
https://wesbos.com/destructuring-objects

*/
var atitle = "\n nt-mongo-atlas2.js - test mongo read write to atlas \n";
console.log(`${atitle}`);
var astep = "start";

const { MongoClient } = require("mongodb");
const uri = "mongodb+srv://dbAdmin:u3KpFTzZBEIEQLzY@cluster0.pfjbe.mongodb.net/test-db";
const connectOptions = {useUnifiedTopology: true};
const client = new MongoClient(uri,connectOptions);
const { ObjectId } = require("mongodb").ObjectId;
var collection = null;
var device = null;
var database = null;
var storageKWH, _id, deviceName, deviceGroup, sumKWH;

async function run() {
try {
await client.connect();
database = client.db("test-db");
collection = database.collection("devices");

await queryDevice();
var {_id, deviceName, deviceGroup, storageKWH} = device;
console.log(`device found = ${deviceName} _id: ${_id}`);

sumKWH = storageKWH + 75;
console.log(` after energy load, sum of storageKWH = ${sumKWH}`);

await updateDevice(device, sumKWH);
console.log(`device energy load completed`);

} finally {
await client.close();
}
};


// https://docs.mongodb.com/drivers/node/usage-examples/findOne
async function queryDevice() {
console.log(`queryDevice called`);
// Query for a movie that has the title 'The Room'
// var query = { deviceName: "solar panel 3000 MW v4" };
var oid1 = new ObjectId("6000908b07564302da69e742");
var query = { _id: oid1};
var options = {
// sort matched documents in descending order by rating
sort: { deviceName: -1 },
// Include only the `title` and `imdb` fields in the returned document
projection: { _id: 1, deviceName: 1, deviceGroup: 1, storageKWH: 1 },
};
// console.log(`query = ${query}`);
device = await collection.findOne(query, options);
// since this method returns the matched document, not a cursor, print it directly
};

// https://docs.mongodb.com/drivers/node/usage-examples/updateOne
async function updateDevice(device, sumKWH) {
var {_id, deviceName, deviceGroup, storageKWH} = device;
var oid1 = new ObjectId(_id);
var filter = {_id: oid1}
var options = {
upsert: true
};
var updateDoc = {
$set: {
storageKWH: sumKWH,
energyStatus: "loaded"
},
};
const result = await collection.updateOne(filter, updateDoc, options );
console.log(`updateDevice "${deviceName}"" matched ${result.matchedCount} count completed with ${sumKWH}`);
};

run().catch(console.dir);

Key Libraries for NodeJS

https://leanylabs.com/blog/npm-packages-for-nodejs/

https://docs.google.com/document/d/1qruyE1PxGCUyv0s7ggYFw59Jd1WizVTv7chmjMIBDoc/edit?usp=sharing

Other NodeJS libraries 

MD5 hash

https://gist.github.com/kitek/1579117

var data = "do shash'owania";
var crypto = require('crypto');
crypto.createHash('md5').update(data).digest("hex");

https://ourcodeworld.com/articles/read/1547/how-to-create-md5-hashes-in-javascript

// contains: "80244576c6c4e060a8e14b124cebaaa4"
// md5("key", "value")
let hash = md5("carlos", "ourcodeworld");

Potential Value Opportunities

Potential Challenges

Node app tests 

• using nvm, install node, npm
• in GitHub, select a repo branch > open terminal on repo > 
• source  ./.bashrc  ( to set node env ) 
• npm install // installs correct mods
• npm start // should open first page in Chrome 

NPM start with environment values

NPM ( or Yarn ) can take NODE_ENV values on the cmd line

NODE_ENV=devLocal PORT=3030 npm start

NPM start from shell script passing a config file for environment

use of custom scripts in ebc-frontend app ok

runnpm.sh -f config/.env.dev
runnpm.sh -f config/.env.devLocal

runnpm.sh -f config/.env.qa

> npm start
> load the config for the environment

.env.dev
ENV_NAME=dev

Node app web page submit fails with CORS error

has been blocked by CORS policy

Access to XMLHttpRequest at 'https://ebc-api-dev.sysopsnetwork.com/authentication' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

What domain are you making your XMLHttpRequest from and to? CORS is a client-side operation; first you need to identify (1) what page is making the blocked XMLHttpRequest and then where it is making the request to. The error you pasted seem incomplete, so I'm not clear on how to help. Also it would help if you also included which domain the above Express code is running under as well.

https://github.com/expressjs/cors/issues/184

example CORS access control error

I am making request from UI(https://localhost://3200) to Node js route(/login) running on (localhost://8090), after hitting node js I am making a call to Single-sign-on using SAML methods, in respone I am receiving URL(https://sso.dol.gov), after receiving URL I am using response.redirect(https://sso.dol.gov). This is when I am getting error.

@dougwilson

Member
dougwilson commented on Jan 28, 2020
Gotcha. So which one of those parts are using XMLHttpRequest? It sounds to me based on your description like the XMLHttpRequest is the request to localhost:8090, which is redirected to sso.dol.gov. If this is the case, the sso.dol.gov domain is what needs CORS policy applied to it to allow calls from localhost:3200.

If this is the case, the sso.dol.gov domain is what needs CORS policy applied to it to allow calls from localhost:3200.

Handling CORS error in Nodejs

https://stackabuse.com/handling-cors-with-node-js/

Candidate Solutions

Magic Nodejs REST Angular CRUD generator - 600 per server

https://polterguy.github.io/

see demo - looks good

server pricing may be an issue except for smaller accounts on cloud or on-prem

Magic will read metadata from your database. It will use this metadata to generate an HTTP REST Web API for you, wrapping all CRUD operations inside of REST endpoints. Then it will use metadata from the REST API to automatically generate Angular components, router links, menu items, datagrids, etc. The end result becomes that before you’ve even had to create as much as a single line of code yourself, 90% of your job is already done.

The resulting frontend gives you a datagrid for all your database tables, allowing you to create, read, update and delete records in your database. It also automatically creates paging, sorting, and filtering for you - In addition to providing you with a very, very, very secure authentication and authorisation system.

Magic is built in .Net Core, and allows you to add C# controllers to it easily. It’s a highly modular architecture, allowing you to intercept its core, using adapters and triggers. The Angular code also perfectly follows all TSLint rules, making it highly readable and easily modified.

sample record edit screen

Prereqs 

The simplest way to get started, is to download its latest release, and use it as a "starter kit". You will need.

1. .Net Core CLI version 3.x or more
2. Some sort of database server Mysql or MS SQL
3. NodeJS
4. Install Angular in a terminal window with npm install -g @angular/cli
5. Magic

To start the Magic dashboard type dotnet run in the "magic.backend" folder. Then type npm link in your "frontend" folder. Start the Magic dashboard by typing ng serve in the "frontend" folder. Go to http://localhost:4200.

Documentation

Although documentation is work in progress, you can rapidly teach yourself the basics here.

• Main documentation website

License

Although most of Magic's source code is publicly available, Magic is not Open Source or Free Software. You have to obtain a valid license key to install it in production, and I normally charge a fee for such a key. You can obtain a license key here. Notice, 5 hours after you put Magic into production, it will stop working, unless you have a valid license for it.

Profound.js for IBMi brings Nodejs services to iSolutions

https://www.profoundlogic.com/profoundjs/

Quickly and easily add powerful Node.js capabilities to your IBM i business apps

Free products

Node.js Framework

Visual Designer

Billable products

Profound.js Connector

Harcon - Nodejs microservices integration

https://www.npmjs.com/package/harcon

harcon is a microservice solution for NodeJS/Browser giving superior abstraction layer for interoperability between entities in a highly structured and fragmented ecosystem. It allows you to design and implement complex workflows and microservices where context and causality of messages are important.

Not as powerful as an ESB but useful for multiple microservices similar to a service mesh for Nodejs

The library has a stunning feature list beyond basic messaging functionality.

• Channel-agnostic: harcon represents a very abstract messaging framework allowing you to use any underlaying technology your application requires: AMQP, MQTT, Amazon SQS, NATS etc... For amqp integration, please check this: harcon-amqp For sqs integration, please check this: harcon-sqs For mqtt integration, please check this: harcon-mqtt For nats.io integration, please check this: harcon-nats

• Tracking: you can monitor every message delivered (request or response) by only few lines of code

• Flow control / Reproducibility: A flow of communication / messages can be halted / continued / reinitiated anytime with no effort

• Free orchestration: your system can be orchestrated and distributed as you wish, message delivery is not limited to nodes or hosts

• Short learning curve: no need to learn hundred of pages, communication has to be simple after all

• Log-free coding: no more mixture of logging and business logic. Harcon logs all messages exchanged.

• Transparent: although harcon introduces lots of complex types and structures, your code will be kept clean and pure, everything is (un)packed in the background in a transparent way

• Smooth infiltration: your objects / functions will possess the necessary services via injection, no need to create complex structures and compounds

• Advanced routing & listening: system fragmentation, qualified names, regular expressions, wildcards, etc.

• Execution-chain: toolset to easily define execution paths between entities to relay messages and results.

• Business-transaction: small helpers to manage business executions paths as (distributed) transactions.

!Note: Harcon's concept is to introduce a clean and high abstraction layer over messaging between entities. Like in case of every abstraction tool, for webapps which are simple as 1, it can be proven as a liability.

This library starts to shine in a highly structured and distributed environment.

Harcon Message Semantics

harcon distinguishes three message flow:

• request: entity A sends a message to B and requests an answer. Normal RPC model.
• inform: entity A sends a message to B and continues right away not considering whether B even received / processed the message. Signals / notifications are meant to be realised.
• delegate: entity A sends a message to B and requests an answer to a specified address. Usual delegation model.

These flows are available as services for all entities within harcon.

Unique messages

Every communication exchanged possesses the following properties (not exclusively):

• unique ID
• reference to the parent message if exists
• uniqued ID of the workflow itself
• external ID of the workflow started by an external communication involving a reference number to consider
• timestamp

Any time you sends a message or receives an answer, such objects are bypassing through the harcon system which logs and tracks all of them.

Step-by-step guide for Example

sample code block

Recommended Next Steps

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