universalify

What is universalify?

The universalify npm package is designed to convert callback-based functions to ones that return promises, allowing for both callback and promise-based usage. This is particularly useful for supporting legacy code while taking advantage of the benefits of promises in newer code.

What are universalify's main functionalities?

fromCallback

Converts a function that uses a callback to one that returns a promise, but still supports the callback interface.

const universalify = require('universalify');
const fs = require('fs');
const readFileAsync = universalify.fromCallback(fs.readFile);

// Using as a promise
readFileAsync('example.txt', 'utf8').then(contents => {
  console.log(contents);
}).catch(error => {
  console.error('Error reading file:', error);
});

// Using with a callback
readFileAsync('example.txt', 'utf8', (error, contents) => {
  if (error) {
    console.error('Error reading file:', error);
    return;
  }
  console.log(contents);
});

fromPromise

Converts a promise-returning function to one that supports both promises and callbacks.

const universalify = require('universalify');
const fsPromises = require('fs').promises;
const readFile = universalify.fromPromise(fsPromises.readFile);

// Using as a promise
readFile('example.txt', 'utf8').then(contents => {
  console.log(contents);
}).catch(error => {
  console.error('Error reading file:', error);
});

// Using with a callback
readFile('example.txt', 'utf8', (error, contents) => {
  if (error) {
    console.error('Error reading file:', error);
    return;
  }
  console.log(contents);
});

Other packages similar to universalify

pify

Pify is a package that promisifies functions. It converts functions that use node-style callbacks into functions that return promises. Unlike universalify, pify does not maintain callback support once promisified.

bluebird

Bluebird is a comprehensive promise library that includes a promisify feature to convert callback-based functions into promise-returning functions. It is more feature-rich than universalify but also larger in size and does not support callbacks after promisification.

util.promisify

Util.promisify is a built-in Node.js utility function that converts a callback-based function into a promise-based one. It is similar to universalify but is limited to Node.js and does not support the original callback interface after conversion.

README

universalify

Make a callback- or promise-based function support both promises and callbacks.

Uses the native promise implementation.

Installation

npm install universalify

API

universalify.fromCallback(fn)

Takes a callback-based function to universalify, and returns the universalified function.

Function must take a callback as the last parameter that will be called with the signature (error, result). universalify does not support calling the callback with three or more arguments, and does not ensure that the callback is only called once.

function callbackFn (n, cb) {
  setTimeout(() => cb(null, n), 15)
}

const fn = universalify.fromCallback(callbackFn)

// Works with Promises:
fn('Hello World!')
.then(result => console.log(result)) // -> Hello World!
.catch(error => console.error(error))

// Works with Callbacks:
fn('Hi!', (error, result) => {
  if (error) return console.error(error)
  console.log(result)
  // -> Hi!
})

universalify.fromPromise(fn)

Takes a promise-based function to universalify, and returns the universalified function.

Function must return a valid JS promise. universalify does not ensure that a valid promise is returned.

function promiseFn (n) {
  return new Promise(resolve => {
    setTimeout(() => resolve(n), 15)
  })
}

const fn = universalify.fromPromise(promiseFn)

// Works with Promises:
fn('Hello World!')
.then(result => console.log(result)) // -> Hello World!
.catch(error => console.error(error))

// Works with Callbacks:
fn('Hi!', (error, result) => {
  if (error) return console.error(error)
  console.log(result)
  // -> Hi!
})

License

MIT