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How one can use the File System in Node.js — SitePoint

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How one can use the File System in Node.js — SitePoint

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Net purposes don’t at all times want to write down to the file system, however Node.js supplies a complete software programming interface (API) for doing so. It could be important for those who’re outputting debugging logs, transferring information to or from a server, or creating command line instruments.

Studying and writing information from code shouldn’t be essentially tough, however your software shall be extra sturdy for those who do the next:

  1. Guarantee it’s cross-platform

    Home windows, macOS, and Linux deal with information otherwise. For instance, you utilize a ahead slash / to separate directories in macOS and Linux, however Home windows makes use of a backslash and bans sure file title characters corresponding to : and ?.

  2. Double-check all the pieces!

    Customers or different apps may delete a file or change entry permissions. All the time verify for such points and deal with errors successfully.

Desk of Contents

The Node.js fs Module

The Node.js fs module supplies strategies for managing information and directories. If you happen to’re utilizing different JavaScript runtimes:

All JavaScript runtimes run on a single processing thread. The underlying working system handles operations corresponding to file studying and writing, so the JavaScript program continues to run in parallel. The OS then alerts the runtime when a file operation is full.

The fs documentation supplies an extended checklist of capabilities, however there are three basic varieties with related capabilities, which we’ll take a look at subsequent.

1. Callback capabilities

These capabilities take a completion callback perform as an argument. The next instance passes an inline perform which outputs the content material of myfile.txt. Assuming no errors, its content material shows after finish of program seems within the console:

import { readFile } from 'node:fs';

readFile('myfile.txt', { encoding: 'utf8' }, (err, content material) => {
  if (!err) {
    console.log(content material);
  }
});

console.log('finish of program');

Be aware: the { encoding: 'utf8' } parameter ensures Node.js returns a string of textual content content material moderately than a Buffer object of binary knowledge.

This turns into difficult when it is advisable run one after one other and descend into nested callback hell! It’s additionally straightforward to write down callback capabilities which look right however trigger reminiscence leaks which are tough to debug.

Most often, there’s little cause to make use of callbacks at this time. Few of the examples beneath use them.

2. Synchronous capabilities

The “Sync” capabilities successfully ignore Node’s non-blocking I/O and supply synchronous APIs such as you’d discover in different programming languages. The next instance outputs the content material of myfile.txt earlier than finish of program seems within the console:

import { readFileSync } from 'node:fs';

strive {
  const content material = readFileSync('myfile.txt', { encoding: 'utf8' });
  console.log(content material);
}
catch {}

console.log('finish of program');

It seems to be simpler, and I’d by no means say don’t use Sync … however, erm … don’t use Sync! It halts the occasion loop and pauses your software. That could be fantastic in a CLI program when loading a small initialization file, however take into account a Node.js net software with 100 concurrent customers. If one person requests a file which takes one second to load, they wait one second for a response — and so do all the opposite 99 customers!

There’s no cause to make use of synchronous strategies when we have now promise capabilities.

3. Promise capabilities

ES6/2015 launched guarantees. They’re syntactical sugar on callbacks to offer a sweeter, simpler syntax, particularly when used with async/await. Node.js additionally launched a ‘fs/guarantees’ API which seems to be and behaves in an analogous option to the synchronous perform syntax however stays asynchronous:

import { readFile } from 'node:fs/guarantees';

strive {
  const content material = await readFile('myfile.txt', { encoding: 'utf8' });
  console.log(content material);
}
catch {}

console.log('finish of program');

Be aware using the 'node:fs/guarantees' module and the await earlier than readFile().

Most examples beneath use the promise-based syntax. Most don’t embody strive and catch for brevity, however it’s best to add these blocks to deal with errors.

ES module syntax

The examples on this tutorial additionally use ES Modules (ESM) import moderately than the CommonJS require. ESM is the usual module syntax supported by Deno, Bun, and browser runtimes.

To make use of ESM in Node.js, both:

  • title your JavaScript information with a .mjs extension
  • use an --import=module change on the command line — corresponding to node --import=module index.js, or
  • you probably have a mission bundle.json file, add a brand new "sort": "module" setting

You may nonetheless use CommonJS require ought to it is advisable.

Studying Information

There are a number of capabilities for studying information, however the easiest is to learn a complete file into reminiscence utilizing readFile, as we noticed within the instance above:

import { readFile } from 'node:fs/guarantees';
const content material = await readFile('myfile.txt', { encoding: 'utf8' });

The second choices object can be a string. It defines the encoding: set 'utf8' or one other textual content format to learn the file content material right into a string.

Alternatively, you’ll be able to learn strains one by one utilizing the readLines() methodology of the filehandle object:

import { open } from 'node:fs/guarantees';

const file = await open('myfile.txt');

for await (const line of file.readLines()) {
  console.log(line);
}

There are additionally extra superior choices for studying streams or any variety of bytes from a file.

Dealing with File and Listing Paths

You’ll typically wish to entry information at particular absolute paths or paths relative to the Node software’s working listing. The node:path module supplies cross-platform strategies to resolve paths on all working methods.

The path.sep property returns the listing separator image — on Home windows or / on Linux or macOS:

import * as path from 'node:path';

console.log( path.sep );

However there are extra helpful properties and capabilities. be part of([…paths]) joins all path segments and normalizes for the OS:

console.log( path.be part of('/mission', 'node/example1', '../example2', 'myfile.txt') );

resolve([…paths]) is comparable however returns the total absolute path:

console.log( path.resolve('/mission', 'node/example1', '../example2', 'myfile.txt') );

normalize(path) resolves all listing .. and . references:

console.log( path.normalize('/mission/node/example1/../example2/myfile.txt') );

relative(from, to) calculates the relative path between two absolute or relative paths (based mostly on Node’s working listing):

console.log( path.relative('/mission/node/example1', '/mission/node/example2') );

format(object) builds a full path from an object of constituent components:

console.log(
  path.format({
    dir: '/mission/node/example2',
    title: 'myfile',
    ext: 'txt'
  })
);

parse(path) does the alternative and returns an object describing a path:

console.log( path.parse('/mission/node/example2/myfile.txt') );

Getting File and Listing Data

You typically must get details about a path. Is it a file? Is it a listing? When was it created? When was it final modified? Are you able to learn it? Are you able to append knowledge to it?

The stat(path) perform returns a Stats object containing details about a file or listing object:

import { stat } from 'node:fs/guarantees';

const data = await stat('myfile.txt');
console.log(data);

It additionally supplies helpful strategies, together with:

const isFile = data.isFile(); 
const isDirectory = data.isDirectory(); 

The entry(path) perform checks whether or not a file might be accessed utilizing a particular mode set through a fixed. If the accessibility verify is profitable, the promise fulfills with no worth. A failure rejects the promise. For instance:

import { entry, constants } from 'node:fs/guarantees';

const data = {
  canRead: false,
  canWrite: false,
  canExec: false
};


strive {
  await entry('myfile.txt', constants.R_OK);
  data.canRead = true;
}
catch {}


strive {
  await entry('myfile.txt', constants.W_OK);
  data.canWrite = true;
}
catch {}

console.log(data);

You may check a couple of mode, corresponding to whether or not a file is each readable and writeable:

await entry('myfile.txt', constants.R_OK | constants.W_OK);

Writing Information

writeFile() is the only perform to asynchronously write a complete file changing its content material if it already exists:

import { writeFile } from 'node:fs/guarantees';
await writeFile('myfile.txt', 'new file contents');

Go the next arguments:

  1. the file path
  2. the file content material — generally is a String, Buffer, TypedArray, DataView, Iterable, or Stream
  3. an elective third argument generally is a string representing the encoding (corresponding to 'utf8') or an object with properties corresponding to encoding and sign to abort the promise.

An analogous appendFile() perform provides new content material to the tip of the present file, creating that file if it doesn’t exist.

For the adventurous, there’s a file handler write() methodology which lets you exchange content material inside a file at a particular level and size.

Creating Directories

The mkdir() perform can create full listing buildings by passing an absolute or relative path:

import { mkdir } from 'node:fs/guarantees';

await mkdir('./subdir/temp', { recursive: true });

You may cross two arguments:

  1. the listing path, and
  2. an elective object with a recursive Boolean and mode string or integer

Setting recursive to true creates the entire listing construction. The instance above creates subdir within the present working listing and temp as a subdirectory of that. If recursive had been false (the default) the promise would reject if subdir weren’t already outlined.

The mode is the macOS/Linux person, group, and others permission with a default of 0x777. This isn’t supported on Home windows and ignored.

The same .mkdtemp() perform is comparable and creates a singular listing sometimes for momentary knowledge storage.

Studying Listing Contents

.readdir() reads the content material of a listing. The promise fulfills with an array containing all file and listing names (apart from . and ..). The title is relative to the listing and doesn’t embody the total path:

import { readdir } from 'node:fs/guarantees';

const information = await readdir('./'); 
for (const file of information) {
  console.log(file);
}


You may cross an elective second parameter object with the next properties:

  • encoding — the default is an array of utf8 strings
  • recursive — set true to recursively fetch all information from all subdirectories. The file title will embody the subdirectory title(s). Older editions of Node.js could not present this selection.
  • withFileType — set true to return an array of fs.Dirent objects which incorporates properties and strategies together with .title, .path, .isFile(), .isDirectory() and extra.

The choice .opendir() perform permits you to asynchronously open a listing for iterative scanning:

import { opendir } from 'node:fs/guarantees';

const dir = await opendir('./');
for await (const entry of dir) {
  console.log(entry.title);
}

Deleting Information and Directories

The .rm() perform removes a file or listing at a specified path:

import { rm } from 'node:fs/guarantees';

await rm('./oldfile.txt');

You may cross an elective second parameter object with the next properties:

  • power — set true to not elevate an error when the trail doesn’t exist
  • recursive — set true to recursively delete a listing and contents
  • maxRetries — make a variety of retries when one other course of has locked a file
  • retryDelay — the variety of milliseconds between retries

The same .rmdir() perform solely deletes directories (you’ll be able to’t cross a file path). Equally, .unlink() solely deletes information or symbolic hyperlinks (you’ll be able to’t cross a listing path).

Different File System Features

The examples above illustrate the most-used choices for studying, writing, updating, and deleting information and directories. Node.js additionally supplies additional, lesser-used choices corresponding to copying, renaming, altering possession, altering permissions, altering date properties, creating symbolic hyperlinks, and expecting file adjustments.

It could be preferable to make use of the callback-based API when expecting file adjustments, as a result of it’s much less code, simpler to make use of, and might’t halt different processes:

import { watch } from 'node:fs';


watch('./mydir', { recursive: true }, (occasion, file) => {

  console.log(`occasion: ${ occasion }`);

  if (file) {
    console.log(`file modified: ${ file }`);
  }

});


The occasion parameter obtained by the callback is both 'change' or 'rename'.

Abstract

Node.js supplies a versatile and cross-platform API to handle information and directories on any working system the place you should utilize the runtime. With slightly care, you’ll be able to write sturdy and transportable JavaScript code that may work together with any file system.

For extra info, confer with the Node.js fs and path documentation. Different helpful libraries embody:

  • OS to question working oystem info
  • URL to parse a URL, maybe when mapping to and from file system paths
  • Stream for dealing with giant information
  • Buffer and TypedArray objects to deal with binary knowledge
  • Baby processes to spawn a subprocess to deal with long-running or complicated file manipulation capabilities.

You may also discover higher-level file system modules on npm, however there’s no higher expertise than writing your personal.

FAQs on Accessing the File System in Node.js

What’s the File System module in Node.js?

The File System module, sometimes called fs, is a core module in Node.js that gives strategies and performance for interacting with the file system, together with studying and writing information.

How can I embody the fs module in a Node.js script?

You may embody the fs module by utilizing the require assertion, like this: const fs = require('fs');. This makes all fs strategies obtainable in your script.

What’s the distinction between synchronous and asynchronous file operations in Node.js?

Synchronous file operations block the Node.js occasion loop till the operation is accomplished, whereas asynchronous operations don’t block the occasion loop, permitting your software to stay responsive. Asynchronous operations are sometimes beneficial for I/O duties.

How do I learn the contents of a file in Node.js utilizing the fs module?

You should utilize the fs.readFile() methodology to learn the contents of a file. Present the file path and a callback perform to deal with the information as soon as it’s learn.

What’s the objective of the callback perform when working with the fs module in Node.js?

Callback capabilities in fs operations are used to deal with the results of asynchronous file operations. They’re known as when the operation is full, passing any errors and knowledge as arguments.

How can I verify if a file exists in Node.js utilizing the fs module?

You should utilize the fs.existsSync() methodology to verify if a file exists at a specified path. It returns true if the file exists and false if it doesn’t.

What’s the fs.createReadStream() methodology, and when is it helpful?

fs.createReadStream() is used for studying giant information effectively. It creates a readable stream for the desired file, permitting you to learn and course of knowledge in smaller, manageable chunks.

Can I take advantage of the fs module to create and write to a brand new file in Node.js?

Sure, you should utilize the fs.writeFile() or fs.createWriteStream() strategies to create and write to a brand new file. These strategies mean you can specify the file path, content material, and choices for writing.

How do I deal with errors when working with the fs module in Node.js?

It is best to at all times deal with errors by checking the error parameter within the callback perform supplied to asynchronous fs strategies or by utilizing strive/catch blocks for synchronous operations.

Is it doable to delete a file utilizing the fs module in Node.js?

Sure, you should utilize the fs.unlink() methodology to delete a file. Present the file path and a callback perform to deal with the consequence.

Can I take advantage of the fs module to work with directories and folder buildings in Node.js?

Sure, the fs module supplies strategies to create, learn, and manipulate directories, together with creating directories, itemizing their contents, and eradicating directories.

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