readFile
- Node.js course
- Beginner
- Lesson 101/116
- 5 min
Learn to read files with fs.readFile.
Read with readFile
fs.readFile reads a file asynchronously and returns a Promise. If you pass 'utf8' as the second argument the result comes back as a string; without it you get a Buffer.
import fs from 'fs/promises';
const data = await fs.readFile('notes.txt', 'utf8');
console.log(data);Here readFile loads the entire file into memory; it suits small and medium files. For very large files createReadStream reduces memory use. If the file is missing the Promise rejects with an ENOENT error.
Practice Your turn: read content with readFile
Start with import fs from 'fs/promises'. Define an async function run(). First write with await fs.writeFile('notes.txt', 'hello world'). Then read with const data = await fs.readFile('notes.txt', 'utf8') and log with console.log(data). Call run().
Starter code
// Import fs/promises
// Define async function run
// Write with writeFile, read with readFile, log with console.log
// Call runSample solution
import fs from 'fs/promises';
async function run() {
await fs.writeFile('notes.txt', 'hello world');
const data = await fs.readFile('notes.txt', 'utf8');
console.log(data);
}
run();Expected output
hello world
Error handling
If the file is missing, fs.readFile returns a rejected Promise and throws an ENOENT error. You can catch it with try/catch, so a missing file leads to an alternative path.
try {
const data = await fs.readFile('missing.txt', 'utf8');
} catch (err) {
console.error('file missing');
}This is a common pattern in file work. If err.code is 'ENOENT' the file was not found; another code means a different problem. Catching errors keeps the application running instead of crashing.
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Fill in the blank: readFile
const data = await fs.____('notes.txt', 'utf8');
console.log(data);const data = await fs.readFile('notes.txt', 'utf8');
console.log(data);Explanation: You read the file with readFile.
2 What does the 'utf8' argument do in fs.readFile?
- It compresses the file
- It makes the result return as a string Correct answer
- It locks the file
- It makes the call synchronous
Explanation: The utf8 argument returns the result as a string.
3 readFile concepts
| Term | Meaning |
|---|---|
readFile |
reads a file |
utf8 |
returns as string |
ENOENT |
file not found |