Node 8 util.promisfy

Example usage of the util.promisfy function that was introduced in Node 8

June 18, 2017 - 1 minute read -

Node 8 added a promisify function to the util core module. A couple of simple usage examples follow.

Usage with a promise

	const {promisify} = require('util');
	const fs = require('fs');
	const readFile = promisify(fs.readFile);

	readFile('./foo.txt').then(
	fileContents => console.log(fileContents.toString()),
	error => console.error(error)
	);

view raw promisify-basic.js hosted with ❤ by GitHub

	const {promisify} = require('util');
	const fs = require('fs');
	const readFile = promisify(fs.readFile);

	// await can only be used within an async function
	(async () => {
	try {
	const fileContents = await readFile('./foo.txt');
	console.log(fileContents.toString());
	} catch (ex) {
	ex => console.error(error)
	}
	})();

view raw promisify-async.js hosted with ❤ by GitHub

If the callback takes multiple arguments the promise will resolve to an object with a key/value for each argument.

	const {promisify} = require('util');
	const child = require('child_process');
	const exec = promisify(child.exec);

	exec('echo "Hello world"').then(
	result => console.log(result), // Prints { stdout: 'Hello world\n', stderr: '' }
	error => console.error(error)
	);