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How do you read a file in Node.js?

Node.jsJunior~1 min read
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1. Asynchronous reading (via a callback)

Load the built-in fs module:

javascript
import fs from 'fs';

And read the file:

javascript
fs.readFile('./data.txt', 'utf8', (err, data) => { if (err) { console.error('Error reading the file:', err); return; } console.log('File contents:', data); });
  • 'utf8' gets you a string instead of a Buffer.
  • If the file isn't found, you get an ENOENT error.
  • This approach doesn't block the main thread (it's asynchronous).

2. Asynchronous reading with fs/promises (via async/await)

The modern, concise, and preferred option.

javascript
import { readFile } from 'fs/promises'; try { const data = await readFile('./data.txt', 'utf8'); console.log('File contents:', data); } catch (err) { console.error('Error reading the file:', err); }

Advantages:

  • No callbacks, plays nicely with async/await;
  • The code reads "synchronously";
  • A great fit for modern apps (Node 14+).

3. Synchronous reading (blocking)

Sometimes handy at initialization (for example, loading configuration):

javascript
import fs from 'fs'; try { const data = fs.readFileSync('./config.json', 'utf8'); console.log('Configuration:', data); } catch (err) { console.error('Error:', err); }

But:

  • It blocks code execution until the file is read;
  • Not recommended on a server, only for CLI/initialization.

4. Streaming reads (for large files)

If a file is very large (gigabytes), streams are the better choice, they read the file in pieces instead of all at once into memory.

javascript
import fs from 'fs'; const stream = fs.createReadStream('./bigfile.txt', 'utf8'); stream.on('data', chunk => { console.log('Got a chunk of data:', chunk); }); stream.on('end', () => { console.log('Reading finished!'); }); stream.on('error', err => { console.error('Error:', err); });

Advantages:

  • Doesn't load the whole file into memory;
  • Data can be processed as it arrives;
  • Ideal for logs, streaming, HTTP responses.

5. Comparing the approaches

ApproachMethodAsynchronousUse case
Callbackfs.readFile()YesThe basic, older style
Promisefs/promises.readFile()YesThe modern standard
Synchronousfs.readFileSync()NoShort scripts only
Streamfs.createReadStream()YesLarge files

6. Example: reading a JSON file

javascript
import { readFile } from 'fs/promises'; try { const raw = await readFile('./config.json', 'utf8'); const config = JSON.parse(raw); console.log('Config:', config); } catch (err) { console.error('Error reading JSON:', err); }

Node.js doesn't parse JSON automatically, JSON.parse() needs to be called.

In one sentence

To read a file in Node.js, use fs.readFile() (asynchronously), fs/promises.readFile() (via await), or the fs.createReadStream() stream for large files.

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