NodeJS general guide

This post is a collection of notes related to general overview and guides of Nodejs.

How to start a web server

Once you’ve installed Node, create a file named app.js with the following code:

const http = require('http');

const hostname = '127.0.0.1';
const port = 3000;

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World\n');
});

server.listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);
});

To run the app execude node app.js. Once it’s done, you can visit http://localhost:3000 and will see a ‘Hello World’.

How to send/handle HTTP requests

The http module allows Node.js to transfer data over HTTP. The module is responsible for:

  • Building web servers
  • Sending client requests
  • Giving responses back to clients
  • Managing connections
  • Holding HTTP constants (methods, status codes)

To include the HTTP module, use the require() method:

var http = require('http');

The following code will send a GET request to NASA’s API and print out the URL for the astronomy picture of the day as well as an explanation:

const https = require('https');

https.get('https://api.nasa.gov/planetary/apod?api_key=DEMO_KEY', (resp) => {
  let data = '';

  // A chunk of data has been recieved.
  resp.on('data', (chunk) => {
    data += chunk;
  });

  // The whole response has been received. Print out the result.
  resp.on('end', () => {
    console.log(JSON.parse(data).explanation);
  });

}).on("error", (err) => {
  console.log("Error: " + err.message);
});

Other ways to make HTTP requests

Request

First install the package npm install request. Then a request can be made like this:

const request = require('request');

request('https://api.nasa.gov/planetary/apod?api_key=DEMO_KEY', { json: true }, (err, res, body) => {
  if (err) { return console.log(err); }
  console.log(body.url);
  console.log(body.explanation);
});

Axios

Axios is a Promise based HTTP client for the browser as well as node.js.

To install from npm execute npm install axios.

And to make a request:

const axios = require('axios');

axios.get('https://api.nasa.gov/planetary/apod?api_key=DEMO_KEY')
  .then(response => {
    console.log(response.data.url);
    console.log(response.data.explanation);
  })
  .catch(error => {
    console.log(error);
  });

Got

Got is another Promise based lightweight solution. Again, install as: npm install got.

And the code is:

const got = require('got');

got('https://api.nasa.gov/planetary/apod?api_key=DEMO_KEY', { json: true }).then(response => {
  console.log(response.body.url);
  console.log(response.body.explanation);
}).catch(error => {
  console.log(error.response.body);
});

How to debug a script

Debugging process can be started in nodejs by adding the --inspect flag:

node --inspect index.js

Once it’s done, you will receive the following message:

Debugger listening on ws://127.0.0.1:9229/5f063ae5-c5ea-4371-ad7a-325ac9b25493
For help, see: https://nodejs.org/en/docs/inspector

After that you can open Chrome DevTools > Dedicated DevTools for Nodejs (green icon) > any other tabs with similar debugging experience. No words, just amazing.

Source: https://nodejs.org/en/docs/guides/debugging-getting-started/

How to dockerize an existing Nodejs app

First you have to install either Docker Desktop for Windows (Microsoft Windows 10) or Docker toolbox.

Then create a Dockerfile with the following content:

FROM node:10

# Create app directory
WORKDIR /usr/src/app

# Install app dependencies
# A wildcard is used to ensure both package.json AND package-lock.json are copied
# where available (npm@5+)
COPY package*.json ./

RUN npm install
# If you are building your code for production
# RUN npm ci --only=production

# Bundle app source
COPY . .

EXPOSE 8080
CMD [ "node", "server.js" ]

server.js should be replaced with the file name you “node”.

.dockerignore file is useful to prevent your local modules and debug logs from being copied onto a Docker image:

node_modules
npm-debug.log

Run the docker and build an image using the docker images command:

docker build -t <your username>/node-web-app .

Once the image is built, you can see it in the list:

$ docker images

# Example
REPOSITORY                      TAG        ID              CREATED
node                            10         1934b0b038d1    5 days ago
<your username>/node-web-app    latest     d64d3505b0d2    1 minute ago

Last but not least, run the image you previously built:

docker run -p 49160:8080 -d <your username>/node-web-app

The output of your app can be printed with:

# Get container ID
$ docker ps

# Print app output
$ docker logs <container id>

# Example
Running on http://localhost:8080

Source: https://nodejs.org/en/docs/guides/nodejs-docker-webapp/#creating-a-dockerfile.

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