Basic of nodejs

node js

What is nodejs

It is event driven architecture, lightweight and efficient way of connecting server from FE, non blocking I/O it doesnt have any document, window, instead it has process, global ,

Some commands

process.exit()→ exits the current node

node → runs the node

global.Object → runs whole object

Non blocking function uses calbback function so it takes less time

running a node js application with file

node hello.js

output - ‘Welcome to nodejs’

Note: Below are synchronous files

creating a file

const fs = require('fs'); → require a file syatem to write in txt

fs.writeFileSync('notes.txt', 'My Name is Sujeendra'); → writing a text in .txt

output→ My Name is Sujeendra

appending a file

fs.appendFileSync(‘notes.txt’, I’m a Software Engineer’);

output→ My Name is Sujeendra I’m A Software Engineer

Getting a file from one file to another

util.js

console.log('utils.js');

const name = 'Sujeendra';

module.exports = name;

multiple 



console.log('utils.js');

const name = 'Sujeendra';

const add = function (a, b) {
    return a + b;
}

module.exports = { name, add };

const name = require('./utils');
const validator = require('validator'); 
console.log(name);

output : utils.js

Sujeendra

multiple
const { name, add } = require('./utils');

const sum = add(4, -2);
console.log(name);
console.log(sum);
console.log(validator.isEmail('ht.com'));
console.log(validator.isURL('ht://www.google'));

console.log(process.argv);
console.log(process.argv[2]);

output : utils.js

note - using nodemon we can run the application no need to run node <file> to start
installation --  bun i nodemon

Sujeendra
2
false
false
[
  'C:\\Program Files\\nodejs\\node.exe', -- which folder
  'C:\\Users\\DLT\\Desktop\\node\\notes-app\\app.js', --which file I exceuted
  'Sujeendra' - name
]
Sujeendra

const command = process.argv[2];

if (command === 'add') {
    console.log('Adding note!');
} else if (command === 'remove') {
    console.log('Removing note');
}


note : node app.js add --title="This is my title"
output:
[
  'C:\\Program Files\\nodejs\\node.exe',
  'C:\\Users\\DLT\\Desktop\\node\\notes-app\\app.js',
  'add',
  '--title=This is my title'
]
Adding note!

jsut console.log(yargs.argv);
yargs- used to crate a own command line in node

output:{ _: []--func, '$0'--props: 'app.js' }
note:node app.js add --title="Things I buy"
o/p:{ _: [ 'add' ], title: 'Things I buy', '$0': 'app.js' }

creating a yargs command ---
yargs.command({
    command: "read",
    describe: "Read a note",
    handler: function () {
        console.log('Reading a note!');
    },
});

i/p-- node app.js read
o/p--[
  'C:\\Program Files\\nodejs\\node.exe',
  'C:\\Users\\DLT\\Desktop\\node\\notes-app\\app.js',
  'read'
]
Reading a note!

aegumanet parsing with yargs
{ _: [ 'read' ], '$0': 'app.js' }yargs.command({
    command: "add",
    describe: "Add a new note",
    builder: {
        title: {
            describe: "Note title",
            demandOption: true,
            type: "string",
        },
    },
    handler: function (argv) {
        console.log('Title:' + argv.title);
    },
});
node app.js add --title="Shopping list" --body="Beautiful"
output:'--title=Shopping list' --body="Beautiful"

const dataBuffer = fs.readFileSync('1-json.json'); -- for reading file
const dataJSON = dataBuffer.toString(); -- for converting string
const data = JSON.parse(dataJSON); -- getting the object

data.name = 'Gunther'; -- changing the object name
data.age = 54; -- changing the age

const userJSON = JSON.stringify(data); -- converting back to string

fs.writeFileSync('1-json.json', userJSON);]

Debugging - for debugging use debugger 
chrome://inspect/#devices - for seeing which are active

note:in call stack always main() function runs first

note: __dirname- gives the current directory with path

__filename- give sthe current filename with path