es6-promisify

What is es6-promisify?

The es6-promisify package is a utility that converts callback-based functions to return Promises, making it easier to work with asynchronous code in a more modern and readable way.

What are es6-promisify's main functionalities?

Promisify a single callback-based function

This feature allows you to convert a single callback-based function, such as `fs.readFile`, into a function that returns a Promise. This makes it easier to handle asynchronous operations using modern async/await syntax or Promise chaining.

const promisify = require('es6-promisify');
const fs = require('fs');
const readFileAsync = promisify(fs.readFile);

readFileAsync('example.txt', 'utf8')
  .then(data => console.log(data))
  .catch(err => console.error(err));

Promisify an entire object of callback-based functions

This feature allows you to promisify all functions within an object, such as the `fs` module, so that all of its methods return Promises. This is useful for working with modules that have multiple callback-based methods.

const promisify = require('es6-promisify');
const fs = require('fs');
const fsAsync = promisify(fs);

fsAsync.readFile('example.txt', 'utf8')
  .then(data => console.log(data))
  .catch(err => console.error(err));

Other packages similar to es6-promisify

util.promisify

The `util.promisify` function is a built-in Node.js utility that provides similar functionality to es6-promisify. It converts callback-based functions to return Promises. Since it is built into Node.js, it does not require an additional package installation. However, it is only available in Node.js versions 8.0.0 and above.

bluebird

Bluebird is a fully-featured Promise library that includes a `promisify` method. It offers more advanced features and better performance compared to es6-promisify. Bluebird is a good choice if you need additional Promise utilities and optimizations.

pify

Pify is a lightweight utility that promisifies callback-style functions. It is similar to es6-promisify but offers more customization options, such as filtering which methods to promisify and handling multiple arguments. Pify is a good alternative if you need more control over the promisification process.

README

es6-promisify

Converts callback-based functions to ES6/ES2015 Promises, using a boilerplate callback function.

Install

Install with npm

npm install es6-promisify

Example

const {promisify} = require("es6-promisify");

// Convert the stat function
const fs = require("fs");
const stat = promisify(fs.stat);

// Now usable as a promise!
try {
    const stats = await stat("example.txt");
    console.log("Got stats", stats);
} catch (err) {
    console.error("Yikes!", err);
}

Promisify methods

const {promisify} = require("es6-promisify");

// Create a promise-based version of send_command
const redis = require("redis").createClient(6379, "localhost");
const client = promisify(redis.send_command.bind(redis));

// Send commands to redis and get a promise back
try {
    const pong = await client.ping();
    console.log("Got", pong);
} catch (err) {
    console.error("Unexpected error", err);
} finally {
    redis.quit();
}

Handle multiple callback arguments, with named parameters

const {promisify} = require("es6-promisify");

function test(cb) {
    return cb(undefined, 1, 2, 3);
}

// Create promise-based version of test
test[promisify.argumentNames] = ["one", "two", "three"];
const multi = promisify(test);

// Returns named arguments
const result = await multi();
console.log(result); // {one: 1, two: 2, three: 3}

Provide your own Promise implementation

const {promisify} = require("es6-promisify");

// Now uses Bluebird
promisify.Promise = require("bluebird");

const test = promisify(cb => cb(undefined, "test"));
const result = await test();
console.log(result); // "test", resolved using Bluebird

Tests

Test with tape

$ npm test

Changes from v5.0.0

• Allow developer to specify a different implementations of Promise
• No longer ships with a polyfill for Promise. If your environment has no native Promise you must polyfill yourself, or set promisify.Promise to an A+ compatible Promise implementation.
• Removed support for settings.thisArg: use .bind() instead.
• Removed support for settings.multiArgs: use named arguments instead.

Published under the MIT License.