Node.js

Question 1

What is Node.js?

Answer 1

short version: asynchronous server environment executing JS outside browser

long version: asynchronous event-driven open source server environment that executes JavaScript code outside a web browser

powered by V8 (same JS engine as Chrome browser)

Question 2

What can Node.js be used for?

Answer 2

build back ends for:

• Web applications
• command-line programs
• or any kind of automation that developers wish to perform

Miscellaneous:

• generate dynamic page content
• create, open, read, write, delete, and close files on the server
• collect form data
• add, delete, modify data in your database

Question 3

What is a REPL?

Answer 3

Read-Eval-Print-Loop (REPL)

interactive computer programming environment that takes single user inputs, executes them, and returns the result to the user

executed piecewise

facilitate exploratory programming and debugging because the programmer can inspect the printed result before deciding what expression to provide for the next read

Question 4

When was Node.js created?

Answer 4

2009

Question 5

What back end languages have you heard of?

Answer 5

Python
Java
Ruby
PHP
JS

Question 6

What is a computer process?

Answer 6

the instance of a program that is being executed by 1+ threads

Question 7

Roughly how many computer processes are running on your host operating system (Task Manager or Activity Monitor)?

Answer 7

a lot
400-500 MAC
200ish Windows

Question 8

Why should a full stack Web developer know that computer processes exist?

Answer 8

Full stack Web development is based on making multiple processes work together to form one application.

This will be extremely important when learning about applications made of multiple components:

• clients
• servers
• databases

Question 9

What is the process object in a Node.js program?

Answer 9

global object that provides information about, and control over, the current Node.js process

doesn’t need “ require() “ to access

Question 10

How do you access the process object in a Node.js program?

Answer 10

use variable “process” & dot notation to access properties/methods

process.property

Question 11

What is the data type of process.argv in Node.js?

Answer 11

returns ARRAY containing command line args passed when node launched

argv[0] = process.execpath (useless to us)
argv[1] = path to js file being executed (useless to us)
argv[2+] = addtl command line args passed (USEFUL!)

therefore always start at argv[2] bc thats where actual input starts

Question 12

What is a JavaScript module?

Answer 12

a single js file

Question 13

What values are passed into a Node.js module’s local scope?

Answer 13

all of these values will change for each module:

\_\_dirname ---> string
\_\_filename --> string
exports --> object
module --> object
require --> function

Question 14

Give two examples of truly global variables in a Node.js program.

Answer 14

clear or set Interval(object)
clear or set Timeout(object)
console
process

Question 15

What is the purpose of module.exports in a Node.js module?

Answer 15

export a function to another js file for use

Question 16

How do you import functionality into a Node.js module from another Node.js module?

Answer 16

use REQUIRE to load content of file into memory
const add = require( ' ./jsFileName ');

Question 17

requires() returns what?

Answer 17

module.exports

if it is 1 function, returns the function

if it is object with many functions, will return the object

Question 18

What is the JavaScript Event Loop?

Answer 18

responsible for:

• executing code
• collecting & processing events
• executing queued sub-tasks

Question 19

What is different between “blocking” and “non-blocking” with respect to how code is executed?

Answer 19

blocking: synchronous - any additional JS code in Node.js process must wait until a operation completes
nonblocking: asynchronous - usually has a callback function

Question 20

What is a directory?

Answer 20

a folder on our hard drive that holds files

Question 21

What is a relative file path?

Answer 21

internal path in same directory
file path relative to where you’re currently at

(adding “ ./ “ if in current folder)

Question 22

What is an absolute file path?

Answer 22

the FULL file path to get to a specific file/folder

path from root directory (beginning of hard drive) and every folder it takes to get to the specific file

NOTE: never hardcode an absolute path; it runs on your machine but may not on others due to different file structures

Question 23

What module does Node.js include for manipulating the file system?

Answer 23

fs module (File System)
must [require] it in if fs is needed

Question 24

What method is available in the Node.js fs module for writing data to a file?

Answer 24

fs.writeFile

Question 25

Are file operations using the fs module synchronous or asynchronous?

Answer 25

asynchronous

Question 26

What is NPM?

Answer 26

node package manager allows us to install useful tools/packages into our projects

Question 27

What is a package?

Answer 27

a file or directory that is described by a [ package.json ] file a reusable bit of code - tools, libraries, etc

Question 28

How can you create a package.json with npm?

Answer 28

cd to root directory for your package; use command: npm init --yes

Question 29

What is a dependency and how to you add one to a package?

Answer 29

package references that are used by your library without which it cannot work something that your project needs to work command: npm install packageName

Question 30

What happens when you add a dependency to a package with npm?

Answer 30

npm install packageName => all will install to the node_modules folder node_modules directory is created within root folder

Question 31

npm install

Answer 31

[ npm install ] by itself will read package.json and install all dependencies (if you cloned a project from somewhere)

Question 32

npm new project

Answer 32

npm init -y (to install package.json) npm install package-name (install the rest of the packages) ``` if installed wrong package: npm uninstall package-name (will delete all files from node_module and remove it from dependency list in package.json) ```

Question 33

How do you add express to your package dependencies?

Answer 33

npm install express

Question 34

What Express application method starts the server and binds it to a network PORT?

Answer 34

app.listen(port# (usually a variable), callback function)

Question 35

how to require express in js file

Answer 35

``` const express = require('express') const app = express (); ``` app.method....

Question 36

servers

Answer 36

errors show up where you ran the server (node filename.js) must stop server with ctrl + C app.listen should be the last line in the file [ http POST :3000/path ] is a shortcut

Question 37

How do you mount a middleware with an Express application?

Answer 37

app.use all requests route through that function

Question 38

Which objects does an Express application pass to your middleware to manage the request/response lifecycle of the server?

Answer 38

app.use(req, res, next)

Question 39

What is the appropriate Content-Type header for HTTP messages that contain JSON in their bodies?

Answer 39

application/json

Question 40

What is the significance of an HTTP request's method?

Answer 40

None on its own; Developers give the request significance the request method doesn't do anything unless developer defines what to do (ex/ delete won't delete anything unless code tells it to)

Question 41

What does the express.json() middleware do and when would you need it?

Answer 41

parses for JSON data and stores it in req.body need it when we need to store JSON data input

Question 42

What does express.static() return?

Answer 42

returns a function (function checks for a file to see if it exists, then returns the file) or HTTP 404 if files not found sole purpose is to serve files from static folder

Question 43

What is the local __dirname variable in a Node.js module?

Answer 43

string - absolute path to directory the module is in (or where the folder the file is in)

Question 44

What does the join() method of Node's path module do?

Answer 44

takes 2+ file path segments strings and joins them