Reading and writing files

Reading a file

We can read files on the computer

import fs from 'fs/promises'

// read diary.txt as a utf-8 encoded string
const txt = await fs.readFile('./diary.txt', 'utf-8')
console.log(txt)

Appending to a file

We can add new data to the end of a file

// append 'Learned a skill.' to diary.txt, preceded by a new line
await fs.appendFile('./diary.txt', '\nLearned a skill.')

Overwriting a file

We can write to a file using javascript

// write string 'My diary:' to todos.txt
await fs.writeFile('./diary.txt', 'My diary:')

DANGER

Before you run fs.writeFile, you should know that it overwrites all data at the file path.

Proceed with caution!

File paths

WARNING

Relative file paths are calculated from the location of the terminal, not the location of the code.

To ensure the file path always points to the right place, use this pattern

const path = new URL('./diary.txt', import.meta.url)
await fs.appendFile(path, '\nFixed a typo')

The URL class will construct the absolute path for us by resolving ./diary.txt with import.meta.url, the absolute path to the script being executed.