Node.js File System Module #52

Question 1

How would you require access and interaction with the file system

Answer 1

const fs = require(‘fs’)

Question 2

Memorize at least some of the fs methods or refer back to this later.

Answer 2

• fs.access( ): check if the file exists and Node can access it with its permissions
• fs.appendFile( ): append data to a file. If the file does not exist, it’s created
• fs.chmod( ): change the permissions of a file specified by the filename passed. Related: fs.lchmod( ), fs.fchmod()
• fs.chown( ): change the owner and group of a file specified by the filename passed.

Related: fs.fchown( ),fs.lchown( )
fs.close( ): close a file descriptor
fs.copyFile( ): copies a file
fs.createReadStream( ): create a readable file stream
fs.createWriteStream( ): create a writable file stream
fs.link( ): create a new hard link to a file
fs.mkdir( ): create a new folder
fs.mkdtemp( ): create a temporary directory
fs.open( ): set the file mode
fs.readdir( ): read the contents of a directory
fs.readFile( ): read the content of a file.
• Related: fs.read( )
fs.readlink( ): read the value of a symbolic link
fs.realpath( ): resolve relative file path pointers (., ..) to the full path
fs.rename( ): rename a file or folder
fs.rmdir( ): remove a folder
fs.stat( ): returns the status of the file identified by the filename passed. Related: fs.fstat( ), fs.lstat( )
fs.symlink( ): create a new symbolic link to a file
fs.truncate( ): truncate to the specified length the file identified by the filename passed. Related: fs.ftruncate( )
fs.unlink( ): remove a file or a symbolic link
fs.unwatchFile( ): stop watching for changes on a file
fs.utimes( ): change the timestamp of the file identified by the filename passed. Related: fs.futimes()
fs.watchFile( ): start watching for changes on a file. Related: fs.watch( )
fs.writeFile( ): write data to a file. Related: fs.write( )

Question 3

The full list of methods that can be used under the fs module are asynchronous by default. How would you make them synchronous if needed ?

Answer 3

Append Sync to the method. Example:
For example:

fs. rename( )
fs. renameSync( )
fs. write( )
fs. writeSync( )

Question 4

How can you access the “path” module in Node.js?

Answer 4

Require it as below:

const path = require(‘path’)

Question 5

What is path.sep?

Answer 5

It’s simply the path segment separator /

/ Mac/Linux
\ Windows

Question 6

What does the path.basename( ) method do?

Answer 6

Return the last portion of a path. A second parameter can filter out the file extension:

require(‘path’).basename(‘/test/something’) //something
require(‘path’).basename(‘/test/something.txt’) //something.txt
require(‘path’).basename(‘/test/something.txt’, ‘.txt’) //something

Question 7

What does the path.dirname( ) method do?

Answer 7

Return the directory part of a path:

require(‘path’).dirname(‘/test/something’) // /test
require(‘path’).dirname(‘/test/something/file.txt’) // /test/something

Question 8

What does the path.extname( ) method do?

Answer 8

Return the extension part of a path

require(‘path’).extname(‘/test/something’) // ‘’
require(‘path’).extname(‘/test/something/file.txt’) // ‘.txt’

Question 9

What does the path.isAbsolute( ) method do?

Answer 9

Returns true if it’s an absolute path

require(‘path’).isAbsolute(‘/test/something’) // true
require(‘path’).isAbsolute(‘./test/something’) // false

Question 10

What does the path.join( ) method do?

Answer 10

Joins two or more parts of a path:

const name = 'flavio'
require('path').join('/', 'users', name, 'notes.txt') //'/users/flavio/notes.txt'

Question 11

What does the path.normalize( ) method do?

Answer 11

Tries to calculate the actual path when it contains relative specifiers like . or .., or double slashes:

require(‘path’).normalize(‘/users/flavio/..//test.txt’) ///users/test.txt

Question 12

What does the path.parse( ) method do?

Answer 12

Parses a path to an object with the segments that compose it:

root: the root
dir: the folder path starting from the root
base: the file name + extension
name: the file name
ext: the file extension

Example:

require(‘path’).parse(‘/users/test.txt’)
results in

{
  root: '/',
  dir: '/users',
  base: 'test.txt',
  ext: '.txt',
  name: 'test'
}

Question 13

What does the path.relative( ) method do?

Answer 13

Accepts 2 paths as arguments. Returns the relative path from the first path to the second, based on the current working directory.

Example:

require(‘path’).relative(‘/Users/flavio’, ‘/Users/flavio/test.txt’) //’test.txt’
require(‘path’).relative(‘/Users/flavio’, ‘/Users/flavio/something/test.txt’) //’something/test.txt’

Question 14

What does the path.resolve( ) method do?

Answer 14

You can get the absolute path calculation of a relative path using path.resolve():

path.resolve(‘flavio.txt’) //’/Users/flavio/flavio.txt’ if run from my home folder

By specifying a second parameter, resolve will use the first as a base for the second:

path.resolve(‘tmp’, ‘flavio.txt’)//’/Users/flavio/tmp/flavio.txt’ if run from my home folder

If the first parameter starts with a slash, that means it’s an absolute path:

path.resolve(‘/etc’, ‘flavio.txt’)//’/etc/flavio.txt’

Question 15

What is the main use for the ‘OS’ module? And like other modules, how is it accessed?

Answer 15

This module provides many functions that you can use to retrieve information from the underlying operating system and the computer the program runs on, and interact with it.

REQUIRE
const os = require('os')

Question 16

How can you find what the delimiter sequence is on a user’s machine?

Answer 16

By calling the os.EOL method. It gives the line delimiter sequence. It’s \n on Linux and macOS, and \r\n on Windows.

*This is a key method that assists in handling files.

Question 17

What information does os.constants.signals tell you?

Answer 17

I gives all the constants related to handling process signals, like SIGHUP, SIGKILL and so on.

*This is a key method that assists in handling files.

Question 18

What is os.constants.errno used for?

Answer 18

It sets the constants for error reporting, like EADDRINUSE, EOVERFLOW and more.

*This is a key method that assists in handling files.

Question 19

What does the os.arch( ) method do?

Answer 19

Return the string that identifies the underlying architecture, like arm, x64, arm64.

Question 20

What does the os.cpus( ) method do?

Answer 20

Return information on the CPUs available on your system.

Example:

[ { model: 'Intel(R) Core(TM)2 Duo CPU     P8600  @ 2.40GHz',
    speed: 2400,
    times:
     { user: 281685380,
       nice: 0,
       sys: 187986530,
       idle: 685833750,
       irq: 0 } },
  { model: 'Intel(R) Core(TM)2 Duo CPU     P8600  @ 2.40GHz',
    speed: 2400,
    times:
     { user: 282348700,
       nice: 0,
       sys: 161800480,
       idle: 703509470,
       irq: 0 } } ]

Question 21

What does the os.endianness( ) method do?

Answer 21

Return BE or LE depending if Node was compiled with Big Endian or Little Endian. Huh? Say What?

Question 22

What does the os.freemem( ) method do?

Answer 22

Return the number of bytes that represent the free memory in the system.

Question 23

What does the os.homedir( ) method do?

Answer 23

Return the path to the home directory of the current user.

Example:

‘/Users/flavio’

Question 24

What does the os.hostname( ) method do?

Answer 24

Return the hostname.

Question 25

What does the os.loadavg( ) method do?

Answer 25

Return the calculation made by the operating system on the load average.

It only returns a meaningful value on Linux and macOS.

Example:

[ 3.68798828125, 4.00244140625, 11.1181640625 ]

Question 26

What does the os.networkInterfaces( ) method d

Answer 26

Returns the details of the network interfaces available on your system. The example provided is TL;DR

Just know it provides IP Addresses, MAC Addresses, Network protocols etc.

Question 27

How would you find the OS your user is utilizing?

Answer 27

os.type( )

Question 28

What is the simplest way to read a file with Node.js?

Answer 28

The simplest way to read a file in Node is to use the fs.readFile() method, passing it the file path and a callback function that will be called with the file data (and the error):

Both fs.readFile() and fs.readFileSync() read the full content of the file in memory before returning the data.

This means that big files are going to have a major impact on your memory consumption and speed of execution of the program.

const fs = require(‘fs’)

fs.readFile('/Users/flavio/test.txt', (err, data) => {
  if (err) {
    console.error(err)
    return
  }
  console.log(data)
})

Alternatively, you can use the synchronous version fs.readFileSync():

const fs = require(‘fs’)

try {
  const data = fs.readFileSync('/Users/flavio/test.txt', 'utf8')
  console.log(data)
} catch (err) {
  console.error(err)
}

Question 29

What is the best way to write a file with Node.js?

Answer 29

The easiest way to write to files in Node.js is to use the fs.writeFile() API.

Example:

const fs = require(“fs”)

const content = “Some content!”

fs.writeFile("/Users/flavio/test.txt", content, (err) => {
  if (err) {
    console.error(err)
    return
  }
  //file written successfully
}

Question 30

How can you inspect a file and get information about it?

Answer 30

using the stat() method provided by the fs module.

You call it passing a file path, and once Node gets the file details it will call the callback function you pass, with 2 parameters: an error message, and the file stats:

const fs = require("fs")
fs.stat("/Users/flavio/test.txt", (err, stats) => {
  if (err) {
    console.error(err)
    return
  }
  //we have access to the file stats in `stats`
})

Question 31

How can you check if a directory exists?

Answer 31

Use fs.access() to check if the folder exists and Node can access it with its permissions.

Question 32

How can you create a new directory using Node.ja?

Answer 32

Use fs.mkdir() or fs.mkdirSync() to create a new folder.

const fs = require(‘fs’)

const dir = ‘/Users/flavio/test’

try {
  if (!fs.existsSync(dir)){
    fs.mkdirSync(dir)
  }
} catch (err) {
  console.error(err)
}

Question 33

What if you wanted to read the content of a directory?

Answer 33

Use fs.readdir() or fs.readdirSync to read the contents of a directory.

Example:

const fs = require('fs')
const path = require('path')

const folderPath = '/Users/flavio'
fs.readdirSync(folderPath)

Question 34

How can you rename a directory?

Answer 34

const fs = require(‘fs’)

fs.rename('/Users/flavio', '/Users/roger', err => {
  if (err) {
    console.error(err)
    return
  }
  //done
})

Question 35

How would you remove a directory with node.js?

Answer 35

Use fs.rmdir( ) Luckily, these expressions look a lot like Linux in terms of naming conventions.

Question 36

Yikes this chapter =

Answer 36

BRUTALLY Mindnumbing.