app.use() :

The app.use() function adds a new middleware to the app. Essentially, whenever a request hits your backend, Express will execute the functions you passed to app.use() in order.

`app.use(express.json())`

express.json() is a built in middleware function in Express starting from v4.16.0. It parses incoming JSON requests and puts the parsed data in req.body.
req.body won't work if we do not use this

JSON functions :

app.use(express.json()); // parses incoming JSON requests and puts the parsed data in `req.body`

/* ------------------------------------------------------ */

// JSON.parse() is used to convert JSON to object
const tours = JSON.parse(
  fs.readFileSync(`${__dirname}/dev-data/data/tours-simple.json`)
);

/* ------------------------------------------------------ */

// we are converting tours JSON to string because we can't write an object to a file
fs.writeFile(
  `${__dirname}/dev-data/data/tours-simple.json`,
  JSON.stringify(tours),
  (err) => {
    // to send the response to the client that the tour has been created
    res.status(201).json({
      status: 'success',
      data: {
        tour: newTour,
      },
    });
  }
);

// another example

return res.status(404).json({
      status: 'fail',
      message: 'Invalid ID',
    });

/* ------------------------------------------------------ */

req.body example :

res.status(codes)

200 : OK
201 : Created
204 : No Content (Used when deleteing something)
400 : the server cannot or will not process the request due to something that is perceived to be a client error

500 : Internal Server Error :

const deleteUser = (req, res) => {
  res.status(500).json({
    status: 'error',
    message: 'This route is not yet defined !'
  })
}

req

1. `req.params`

2. `req.body` :

used with post methods
if we post a request with the body :

// json
{ 
    "name": "Test Tout",
    "duration": 10,
    "difficulty": "easy"
}

then req.body will give output as an object :

// js
{ name: 'Test Tout', duration: 10, difficulty: 'easy' }

ESLINT airbnb Config

npm i eslint prettier eslint-config-prettier eslint-plugin-prettier eslint-config-airbnb eslint-plugin-node eslint-plugin-import eslint-plugin-jsx-a11y eslint-plugin-react --save-dev

.eslintrc.json

{
  "extends": ["airbnb", "prettier", "plugin:node/recommended"],
  "plugins": ["prettier"],
  "rules": {
    "prettier/prettier": "error",
    "spaced-comment": "off",
    "no-console": "warn", // eslint does not allow console.log : warn
    "consistent-return": "off", // each function should return something : off
    "func-names": "off",
    "object-shorthand": "off",
    "no-process-exit": "off",
    "no-param-reassign": "off",
    "no-return-await": "off",
    "no-underscore-dangle": "off",
    "class-methods-use-this": "off",
    "prefer-destructuring": ["error", { "object": true, "array": false }],
    "no-unused-vars": ["error", { "argsIgnorePattern": "req|res|next|val" }] // no-unused-vars means that we should not have any unused variables : error
  }
}