The thenify npm package is designed to convert Node.js callback-style functions to functions that return a promise. This is particularly useful when working with older Node.js APIs or third-party libraries that do not natively support promises, allowing developers to write cleaner, more modern asynchronous code using async/await or .then() syntax.

What are thenify's main functionalities?

Converting a callback-style function to a promise-returning function

This feature allows you to wrap a traditional Node.js callback-style function, such as `fs.readFile`, in a way that it returns a promise. This enables the use of `.then()` and `.catch()` for cleaner asynchronous control flow.

const thenify = require('thenify');
const fs = require('fs');
const readFile = thenify(fs.readFile);

readFile('example.txt', 'utf8').then(contents => {
  console.log(contents);
}).catch(err => {
  console.error(err);
});

Other packages similar to thenify

Readme

Source

thenify

Promisify a callback-based function using any-promise.

Preserves function names
Uses a native promise implementation if available and tries to fall back to a promise implementation such as bluebird
Converts multiple arguments from the callback into an Array, also support change the behavior by options.multiArgs
Resulting function never deoptimizes
Supports both callback and promise style

An added benefit is that thrown errors in that async function will be caught by the promise!

API

fn = thenify(fn, options)

Promisifies a function.

Options

options are optional.

options.withCallback - support both callback and promise style, default to false.
options.multiArgs - change the behavior when callback have multiple arguments. default to true.
- true - converts multiple arguments to an array
- false- always use the first argument
- Array - converts multiple arguments to an object with keys provided in options.multiArgs
Turn async functions into promises

var thenify = require('thenify');

var somethingAsync = thenify(function somethingAsync(a, b, c, callback) {
  callback(null, a, b, c);
});

Backward compatible with callback

var thenify = require('thenify');

var somethingAsync = thenify(function somethingAsync(a, b, c, callback) {
  callback(null, a, b, c);
}, { withCallback: true });

// somethingAsync(a, b, c).then(onFulfilled).catch(onRejected);
// somethingAsync(a, b, c, function () {});

or use thenify.withCallback()

var thenify = require('thenify').withCallback;

var somethingAsync = thenify(function somethingAsync(a, b, c, callback) {
  callback(null, a, b, c);
});

// somethingAsync(a, b, c).then(onFulfilled).catch(onRejected);
// somethingAsync(a, b, c, function () {});

Always return the first argument in callback

var thenify = require('thenify');

var promise = thenify(function (callback) {
  callback(null, 1, 2, 3);
}, { multiArgs: false });

// promise().then(function onFulfilled(value) {
//   assert.equal(value, 1);
// });

Converts callback arguments to an object

var thenify = require('thenify');

var promise = thenify(function (callback) {
  callback(null, 1, 2, 3);
}, { multiArgs: [ 'one', 'tow', 'three' ] });

// promise().then(function onFulfilled(value) {
//   assert.deepEqual(value, {
//     one: 1,
//     tow: 2,
//     three: 3
//   });
// });

Keywords

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Last updated on 17 Jun 2020

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