Summary
NodeJS has
fsmodule that helps in managing files'fs' module has Promise API, Callback API, and Synchronous API.
There are various methods in
fsfrom creating, to deleting the files.Always use Async methods over sync for improving performance unless and until you have requirements to use sync methods.
Welcome back to my 2nd blog from the series of NodeJS. If you haven't checked my 1st blog, please check here.
Today we will explore the 2nd module (in-built package) of NodeJS - fs (file system).
We have 3 ways to use fs module in NodeJS:
Promise API
callback API
Synchronous API
| import | mode | return | |
|---|---|---|---|
| Promise | node:fs/promises | promise based (async) | promise |
| Callback | fs | async | error/success or data |
| Synchronous | fs | sync | error/success or data |
In this tutorial we will go through the Callback.
What is fs?
NodeJS has native or built-in package fs. FS stands for filesystem. FS enables devs to create, open, read and write files.
This is an important feature. Developers can do a lot by using FS. Developers will have control over the files.
Where to Use?
fsin configurations.Build Scripts
Temporary data storage
Processing of data before storing in database
How to create a file?
There are 3 ways (methods) to create a new file:
open: open an existing file.writeFile: it will create a file if it's not exist and write content in it.appendFile: it will create a file if it's not exist and append content in it.
How to write content in a file?
- writeFile
file name
data
options: encoding, mode, flag
callback: error or success
// Example: Callback API
const fs = require('fs');
fs.writeFile('logs.txt','hello', 'utf8' (err) => {
if(err) {
console.log('error')
}
else{
console.log('data saved')
}
});
// Example: Promise API
import { writeFile } from 'node:fs/promises';
(async function main() {
try {
await writeFile(
"logs.txt",'hello')
console.log("The written file has"
+ " the following contents:");
} catch (err) {
console.error(err);
}
})();
2 . open
file name
mode
callback: error or success
const fs = require('fs');
// Callback API
fs.open('logs.txt', 'w', (err) => {
if(err) {
console.log('error')
}
else{
console.log('file open')
}
});
// Promise API
import { open } from 'node:fs/promises';
(async function main() {
try {
await open(
"logs.txt")
console.log("The file has been open");
} catch (err) {
console.error(err);
}
})();
3 . appendFile
file name
data
options: encoding, mode, flag
callback: error or success
// callback API
fs.appendFile('logs.txt', 'new text', 'utf8' , (err) => {
if(err) {
console.log('error')
}
else{
console.log('data added')
}
});
// Promise API
import { appendFile } from 'node:fs/promises';
(async function main() {
try {
await appendFile("logs.txt", 'hello');
console.log("The file has been open");
} catch (err) {
console.error(err);
}
})();
How to read content from a file?
So far we saw how to create and write content to a file. We can also read the file's content.
read
file name
encoding options: utf8, utf16, base ,etc.
callback: error or data
fs.readFile('logs.txt', (err,data) => {
if(err) {
console.log('error')
}
else{
console.log(data); // this will return buffer
console.log(data.toString()); // convert the buffer to string
}
});
Code:
// import package
const fs = require('fs')
// read a file
const readfile = fs.readFile('logs.txt', 'utf-8');
console.log(readfile);
// write content of a file
const writefile = fs.writeFile('logs.txt', 'hello');
const readfile = writefile.readFile(writefile)
console.log(readfile);
// append content
const readfile = fs.appendFile('logs.txt', 'utf-8');
console.log(readfile);
// rename
const logs = fs.createFile('logs.txt');
fs.rename('logs.txt', 'userlogs.txt', () => {
console.log('done')
});
// delete
const logs = fs.createFile('logs.txt');
fs.unlink('logs.txt', () => {
console.log('deleted')
});
Important
Content in the file would be either string, buffer, or text. Not, object
writeFile will overwrite the content. Hence, use appendFile
sync vs async
You will see that there are 2 methods in fs: readfile and readFileSync. readFile is async operation. It's a blocking operation and will impact the performance. Hence, prefer to use readFile over readFileSync unless and until you don't have any requirement.
Top comments (1)
Great content
keep it up