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

1var thenify = require('thenify');
2
3var somethingAsync = thenify(function somethingAsync(a, b, c, callback) {
4  callback(null, a, b, c);
5});

• Backward compatible with callback

1var thenify = require('thenify');
2
3var somethingAsync = thenify(function somethingAsync(a, b, c, callback) {
4  callback(null, a, b, c);
5}, { withCallback: true });
6
7// somethingAsync(a, b, c).then(onFulfilled).catch(onRejected);
8// somethingAsync(a, b, c, function () {});

or use thenify.withCallback()

1var thenify = require('thenify').withCallback;
2
3var somethingAsync = thenify(function somethingAsync(a, b, c, callback) {
4  callback(null, a, b, c);
5});
6
7// somethingAsync(a, b, c).then(onFulfilled).catch(onRejected);
8// somethingAsync(a, b, c, function () {});

• Always return the first argument in callback

1var thenify = require('thenify');
2
3var promise = thenify(function (callback) {
4  callback(null, 1, 2, 3);
5}, { multiArgs: false });
6
7// promise().then(function onFulfilled(value) {
8//   assert.equal(value, 1);
9// });

• Converts callback arguments to an object

1var thenify = require('thenify');
2
3var promise = thenify(function (callback) {
4  callback(null, 1, 2, 3);
5}, { multiArgs: [ 'one', 'tow', 'three' ] });
6
7// promise().then(function onFulfilled(value) {
8//   assert.deepEqual(value, {
9//     one: 1,
10//     tow: 2,
11//     three: 3
12//   });
13// });