Summary - fs module

Combine readFile, writeFile and existsSync to write a notes app.

Summary - the fs module

In this group you learned the Node.js fs module. fs/promises provides Promise-based methods; readFile reads, writeFile writes (overwriting), appendFile appends. For existence checks you use existsSync.

In async work you wait with await and catch errors with try/catch. writeFile erases old content; appendFile keeps it. appendFile is ideal for logs and readFile for reading config files.

Exercise Your turn: writeFile + readFile

Start with import fs from 'fs/promises'. Define an async function run(). Inside, write await fs.writeFile('ozet.txt', 'hello'). Then read with const data = await fs.readFile('ozet.txt', 'utf8') and log with console.log(data). Call run().

Show example solution

import fs from 'fs/promises';

async function run() {
  await fs.writeFile('ozet.txt', 'hello');
  const data = await fs.readFile('ozet.txt', 'utf8');
  console.log(data);
}
run();

Exercise Your turn: log with appendFile

Start with import fs from 'fs/promises'. Define an async function run(). First write await fs.writeFile('log.txt', 'start'), then append with await fs.appendFile('log.txt', ' end'). Read with const data = await fs.readFile('log.txt', 'utf8') and log with console.log(data). Call run().

Show example solution

import fs from 'fs/promises';

async function run() {
  await fs.writeFile('log.txt', 'start');
  await fs.appendFile('log.txt', ' end');
  const data = await fs.readFile('log.txt', 'utf8');
  console.log(data);
}
run();

Test yourself

Match the fs methods

readFile

reads a file
writeFile

overwrites
appendFile

appends
existsSync

existence check
Which method fully replaces a file's content (overwrites)?
- fs.appendFile
- fs.writeFile
- fs.readFile
- fs.existsSync
Show answer

fs.writeFile — writeFile erases old content and writes the new.

Next lesson: path.join

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