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Node.js built-in module functions as Promises

Published February 28, 2023Last updated February 4, 20241 min read

Node.js provides asynchronous methods for fs, dns, stream, and timers modules that return Promises.

const {
createWriteStream,
promises: { readFile }
} = require('fs');
const dns = require('dns/promises');
const stream = require('stream/promises');
const timers = require('timers/promises');
const sleep = timers.setTimeout;
const SLEEP_TIMEOUT_MS = 2000;
(async () => {
const fileName = 'test-file';
const writeStream = createWriteStream(fileName, {
autoClose: true,
flags: 'w'
});
await stream.pipeline('some text', writeStream);
await sleep(SLEEP_TIMEOUT_MS);
const readFileResult = await readFile(fileName);
console.log(readFileResult.toString());
const lookupResult = await dns.lookup('google.com');
console.log(lookupResult);
})();

Use the promisify function to convert other callback-based functions to Promise-based.

const crypto = require('crypto');
const { promisify } = require('util');
const randomBytes = promisify(crypto.randomBytes);
const RANDOM_BYTES_LENGTH = 20;
(async () => {
const randomBytesResult = await randomBytes(RANDOM_BYTES_LENGTH);
console.log(randomBytesResult);
})();