Node.js notes part 1

  • In nodejs, the global object is global

    • DOM methods cannot be used

  • To clear setInterval

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    setTimeout(() => {
        clearInteval(interval);
    }, 3000);
    const interval = setInterval(() => {
        console.log('1s');
    }, 1000);

  • To get the dir and file path

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    console.log(__dirname);
    console.log(__filename);

  • Modules & Require

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    const requiring = require('./filename');
    // return an empty object if the required file are not exporting things

    // in the required file
    const people = ['nina', 'gala'];
    module.export = people;
    // so that requring = ['nina', 'gala'];

    • To export multiple things

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      const people = ['nina', 'gala'];
      const age = ['20', '45'];

      module.exports = {
          people: people, // or shortcut: people
          age: age
          // people, age for short
      };

      Or destruct the exported object

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      // in the requring file
      const { people } = require('./people'); // same name required

  • The file system

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    const fs = require('fs');

    // reading files
    fs.readFile('./docs/hello.txt', (err, data) => { // (relativePath, function(ASYN))
        if (err) { console.log(err); }
        console.log(data.toString());
    })
    // For the execution order, while the file is reading, the code moves on

    // writing files
    fs.writeFile('./docs/target.txt', 'the text', () => { // ASYN
        console.log('file was written')
    })

    // directories
    if (!fs.existSync('./assets')) {
        fs.mkdir('./assets', (err) => { // can't create an existing folder
        if (err) {}
        console.log('folder created');
        })
    } else {
        fs.rmdir('', (err) => {

        })
    }

    // deleting files
    // to make sure the file exists
    if (fs.existsSync('./file.txt')) {
        fs.unlink('./file.txt', (err) => {
            if (err){}
        })
    }

  • Streams & Buffers

    • Streams - Start using data, before it has finished loading

    • Buffer - Chunks of data when data is streaming

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      const fs = require('fs');
      // read stream
      const readStream = fs.createReadStream('some file', {encoding: 'utf8'});
      // write stream
      const writeStream = fs.createWriteStream('some file');

      readStream.on('data', (chunk) => { // listen 'data' on the stream
          console.log(chunk);
          writeStream.write('---NEW CHUNK---');
          writeStream.write(chunk);
      })
      // pipe: from a readable stream to a writable one
      readStream.pipe(writeStream); // the same as above

  • Client & Servers - node create a server

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    const http = require('http');

    const server = http.createServer((req, res) => { // store it in case it will be used later
        // respond to every request to the server

    });

    server.listen(3000, 'localhost', () => {
        console.log('listening for requests on port 3000')
    })
    • Localhost is like domain name on the web. localhost → 127.0.0.1 → own computer. It is used when we use our own computer as a server
    • Port numbers: ‘doors’ into a computer

  • Requests & Responses

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    const server = http.createServer((req, res) => {
        // set header content type
        res.setHeader('Content-Type', 'text/plain');
        // return a sentence to the browser
        res.write('hello world');
        res.end();
    })

    // send some HTML
    const server = http.createServer((req, res) => {
        res.setHeader('Content-Type', 'text/html');
        // To add some styles
        res.write('<head><link res="stylesheet" href="#"></head>')
        res.write('<h1>Hello World</h1>');
        res.write('<p>Hi Again</p>');
        res.end();
    })

  • Use seperated HTML files

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    const http = require('http');
    const fs = require('fs');

    const server = http.createServer((req, res) => {
        // set header content type
        fs.readFile('./dir/index.html', (err, data) => {
            if (err) { // if error, keep the request hanging
                console.log(err);
                res.end(); // so end the request
            } else {
                res.write(data);
                res.end();
                // In short: res.end(data);
            }
        });
    })

  • Basic Routing

    • From above, for what route are being requested, we always get the same page. To send different HTML pages depending on different routes.

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      const http = require('http');
      const fs = require('fs');

      const server = http.createServer((req, res) => {

          // To figure out the different routes
          let path = './views/'; // the folder contains HTML pages
          switch(req.url) {
              case '/':
                  path += 'index.html';
                  break;
              case '/about':
                  path+= 'about.html';
                  break;
              default:
                  path += '404.html';
                  break;
          }
          // file operations ...
      })

  • Status Codes

    • The type of response sent to the browser - How successful the request works

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      // 200 - fine
      // 301 - Resource moved
      // 404 - Not found
      // 500 - Internal server error
          switch(req.url) {
              case '/':
                  path += 'index.html';
                  res.statusCode = 200;
                  break;
              case '/about':
                  path+= 'about.html';
                  res.statusCode = 200;
                  break;
              default:
                  path += '404.html';
                  res.statusCode = 404;
                  break;

    • Redirect

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      case '/about-old':
          res.statusCode = 301;
          res.setHeader('Location', '/about');
          res.end();