Process

// Process does not require a "require", it's automatically available.

Exit from a Node program

syntax:


    process.exit(<exit_code>)

Exit codes are as follows:

0: Success
1: Uncaught Fatal Exception
2 (Unused) - reserved for bash
3: Internal JavaScript Parse Error
4: Internal JavaScript Evaluation Failure
5: Fatal Error
6: Non-function Internal Exception Handler
7: Internal Exception Handler Run-Time Failure
8 (Unused)
9: Invalid Argument
10: Internal JavaScript Run-Time Failure
12: Invalid Debug Argument
13: Unfinished Top-Level Await
>128: Signal Exits

// calling process.exit(), results in aborigin any currently pending or running request

Alternatively,


    const server = app.listen(3000, () => console.log('Server ready'))

    process.on('SIGTERM', () => {
        server.close(() => {
            console.log('Process terminated')
        })
    })

Environment Variables


    process.env.<env_var>

Express

Express is a framework that uses the http module under the hood, app.listen() returns an instance of http. You would use https.createServer if you needed to serve your app using HTTPS, as app.listen only uses the http module.

Module

Exports

functionality must be exposed before it can be imported by other files. Any other object or variable defined in the file by default is private

There are 2 ways to export property.

Module.exports exports

exposes the object it points to. exposes the properties of the object it points to

Module.exports	exports
exposes the object it points to.	exposes the properties of the object it points to
`const car = { brand: 'Ford', model: 'Fiesta' } module.exports = car`	`const car = { brand: 'Ford', model: 'Fiesta' } exports.car = car`
`const car = require('./car')`	`const car = require('./items').car`


    const car = { brand: 'Ford', model: 'Fiesta' }
    module.exports = car


    const car = { brand: 'Ford', model: 'Fiesta' }
    exports.car = car


    const car = require('./car')


    const car = require('./items').car

Events

Event Emitter


    /* initialization */
    const EventEmitter = require('events')
    const eventEmitter = new EventEmitter()

    /* callback */
    eventEmitter.on('start', () => {
        console.log('started')
    })

    /* trigger event */
    eventEmitter.emit('start')

Other methods exposed by EventEmitter

once(): add a one-time listener
removeListener() / off(): remove an event listener from an event
removeAllListeners(): remove all listeners for an event