NodeJS

Question 1

What can Node do which old JS can’t?

Answer 1

It can interface with a computer’s hardware, which is why Electron uses node as an example and why it can act as a webserver.

Question 2

How can I enable ES 6 imports in Node

Answer 2

Set the type property in your package.json to module. Typescript can do it by default, as it’s one of its features.

Question 3

What is commonJS

Answer 3

It’s node’s way of importing other files into a different file by using require('./whatever) - extension not required.

In the other file use module.exports = ‘anything’

Anything as a variable:

module.exports = 5;

const number = require(‘./module’);

OR

module.exports = {
someFunction(){

}
}

const {someFunction} = require(‘./someModule’);

someFunction();

const someModule = require(‘./someModule’);
someModule.someFunction()

Question 4

What does a bare-bones express app require

Answer 4

//import express
const express = require(‘express’);

OR import with type=’module’

import express from ‘express’;

const app = express();

app.get(‘/’,(req,res)=>{res.send(‘some content’)})

app.listen(‘3000’);

SETUP body-parser in order to get the POST body from post requests. - makes req.body available

const bodyParser = require(‘body-parser’);

//middleware

app.use(bodyParser.urlencoded({extended:true}));

REMEMBER
Form data is parsed as strings when sent via HTML form

Question 5

Different res methods

Answer 5

These set the response Content-Type header to application/json or text/html.

Second arg is the status code for example 404 - but deprecated

Using res.status(300).send(‘sdffds’) now preferred

res.json() - json
res.send() - html
res.sendFile() - set file path
res.render() - dynamic rendering with ejs for example

Question 6

What is __dirname and it’s purpose

Answer 6

It’s to work with relative file paths.
__dirname refers to the absolute path of the folder of the script that’s executing it.

Question 7

When is __dirname not available?

Answer 7

In ES6 module files, ie, when type in package.json is set to module

Question 8

What does req contain?

Answer 8

req.path - any path variables defined with app.get(‘/blablabla/:someVar/’). Ideal for slugs.

req.body - if body parser is set up

req.query - when query parameters added - users?name=albert

Question 9

How to catch any path not defined and what is important?

Answer 9

With wildcard

It should be at the end of the router script, otherwise sub-sequent paths will not be reached.

app.get(‘,()=>{});
app.post(‘’,()=>{})
app.put(‘’,()=>{})
app.patch(‘,()=>{})
app.delete(‘*’,()=>{})

Question 10

Explain HTTP methods/verbs

Answer 10

POST - to update
PUT - replace data
PATCH - update data
DELETE - removed data
GET - retrieve data

Question 11

What is a popular template engine?

Answer 11

EJS

Question 12

What is a template engine?

Answer 12

It makes it easy, and less dirty, to dynamically generate HTML, with variable values and conditionals

Question 13

How do you configure a public path for static files

Answer 13

This is for serving static items like javascript, images, CSS etc

app.use(express.static(‘public’))

Now all files in the public directory are accessible:

public/styles.css

<link></link>

Question 14

What is middleware in Express

Answer 14

Use app.use() to set middleware

It is a function that is run between the request being received and the response being sent back. It is fired even before the route function.

It allows you to for example do authentication and authorization of routes.

It also allows body-parser for example to intercept the request before it reaches the routes.

Question 15

How to implement middleware function

Answer 15

app.use((req,res,next)=>{
// call next to go to next middleware or eventually the route if there is no subsequent middleware

next();
})

If next() is not invoked or a response is not returned, it will hang until the request times out.

Question 16

Best practice for authentication and authorization

Answer 16

Create middleware for each role, for authentication

Then apply the middleware to the routes/route handlers you want to target via the second arg

app.get(‘/’,middleware,(req,res)=>{

})

or route groups

const myGroup = express.Router();

myGroup.use(someMiddlewareFunction);

myGroup.post(‘/’,(req,res,next) =>res.send());

app.use(‘/a-prefix’,myGroup)

OR

app.use(myGroup)

Question 17

What are route handlers

Answer 17

Handles routes, for example

app.get()
app.post(‘/users’,()=>{})

Question 18

How to create route groups

Answer 18

//useful middlware

const someGroup = express.Router();

someGroup.get();

app.use(‘/some-prefix’,someGroup);

Question 19

How to create route groups

Answer 19

//useful middleware

const someGroup = express.Router();

someGroup.get();

app.use(‘/some-prefix’,someGroup);

Question 20

Writeable and readable streams

Answer 20

Readable streams - can read data in chunks from a readable stream.
Writeable stream - can write chunks of data to a writable stream. This can be a file or the browser, via the response object also being a writable stream.

The readable stream fills up a buffer, which in turn sends the filled buffer’s data to the stream.on(‘data’) event.

const stream = fs.createReadStream(__dirname+’/example.txt’,’utf-8’);
const write = fs.createWriteStream(‘without-pipe.txt’)
const writePipe = fs.createWriteStream(‘with-pipe.txt’)

stream.on('data',chunk=>{
    console.log(chunk);
    write.write(chunk);
})

// shorthand

stream.pipe(writePipe);
stream.pipe(res);

Question 21

What is pipe used for?

Answer 21

You can pipe a readable stream into a writable stream.

readable.pipe(writable)

Question 22

What are buffers?

Answer 22

A buffer is a temporary storage place for data that is being moved from one point to another. Using .toString() on the buffered data will convert it to text.