Node File System Basics
July 1, 2020
Node.js comes with a built-in File System (fs) module that has all the features needed
to perform CRUD operators on local files and folders. First install NodeJS if you haven’t already.
If you want to follow along in the editor, create a index.js file to to run each of the
examples. Import the fs module at the top
const fs = require('fs')We can run this file for each example using
node indexThe file system has a variety of methods available such as opening, editing, deleting files, etc that we can use. Each method has an asynchronous and synchronous version available to use. The shorter method name is always asychronous, while the synchronous one has Sync at the end.
fs.appendFile()is asynchronousfs.appendFileSync()is synchronous
Both methods generally achieve the same thing so choose the one that makes the most sense
for your situation
Here are some of the methods you can call using the fs module
| File system Method | What it does |
|---|---|
| appendFile | Appends text to a file |
| mkdir | Creates a directory (or multiple) |
| readDir | Reads the contents of a directory |
| readFile | Reads a file |
| writeFile | Writes text to a file |
| unlink | Deletes a file |
Each method generally accepts a path or file string as the first argument.
Create Files and Folders
Create Files
To create a new file, use the writeFile method to write a blank string. This will create
a new file if the file doesn’t already exist
fs.writeFile('new.txt', '', err => {
if (err) throw err
})Create folders
Create one or multiple nested folders using the filesystem like so
fs.mkdir('./folder/subfolder', {recursive: true}, err => {
if (err) throw err
})Write to a File
There are two methods to write to a file, depending on if you want to add text or
overwrite text. The first method, writeFile will overwrite whatever text is in a file
fs.writeFile('list.txt', 'apples, oranges, lemons', err => {
if (err) throw err
console.log('File saved!')
})The other method, appendFile will create a new file if it doesn’t exist, and append text
to the end if it does
fs.appendFile('list.txt', 'apples, oranges, lemons', err => {
if (err) throw err
console.log('Text was appended to file!')
})Read Files and Folders
Read a file
We can read our list.txt file from above with the readFile method
fs.readFile('list.txt', function (err, data) {
if (err) {
return console.error(err)
}
console.log('Asynchronous read: ' + data.toString())
})Synchronous methods are sometimes easy to code for example we could shorten the above code to
var data = fs.readFileSync('list.txt')
console.log('Synchronous read: ' + data.toString())Read a folder
We can also read folders with the following readdir method
fs.readdir('./folder', function (err, files) {
if (err) {
return console.error(err)
}
files.forEach(function (file) {
console.log(file)
})
})This method will return the names of the contents of the folder, whether they are files or folders.
Delete Files
Lastly, we can delete files with the unlink method
fs.unlink('list.txt', function (err) {
if (err) {
return console.error(err)
}
console.log('File deleted!')
})Making HTML and JS Files
The fs module is great for working with any types of text files including .txt, .js, and even .html. For example we can include whatever file type we need like so
fs.appendFile(
'index.html',
`<!DOCTYPE html><html>
<head>
<title>Page Title</title>
</head>
<body>
<h1>Page Heading</h1>
</body>
</html>`,
err => {
if (err) throw err
console.log('Text appended to the file!')
},
)There are plenty of cool features in the file system you can use to build out interesting applications such as editors, note-taking apps, and more.