then-callback

then-callback

Wrap a promise to allow passing callback to .then of given promise, also works as normal .then

Install

npm i then-callback --save

Usage

For more use-cases see the tests

thenCallback

Basically, you just pass a promise and it returns promise, but .then from the returned promise can accept a callback function, instead of two arguments as usual - one for result, one for error.
Notice that it also works as normal .then if you pass two arguments.

• <promise> {Promise}
• return {Promise}

Example

const thenCallback = require('then-callback')
const promise = Promise.resolve(123)

thenCallback(promise).then((err, res) => {
  console.log('err:', err) // => null
  console.log('res:', res) // => 123
})

// but also works as normal `.then`
thenCallback(promise).then((res) => {
  console.log('res:', res) // => 123
}, (err) => {
  console.log('err:', err)
})

You just need to wrap a promise, then you can use .then as usual, or to pass callback-style function to it as first argument.

Example

const fs = require('fs')
const redolent = require('redolent')
const readFile = redolent(fs.readFile)
const thenCallback = require('then-callback')

const thenCallback = require('then-callback')
var promise = readFile('package.json', 'utf8')
promise = thenCallback(promise)

promise.then((err, res) => {
  if (err) return console.error(err)
  console.log(JSON.parse(res).name) //=> 'then-callback'
})

Otherwise, if you pass two arguments and second is function, it will work as normal .then.

Example

const thenCallback = require('then-callback')
const NativePromise = require('native-or-another')()

// rejected promise
var promise = NativePromise.reject(new Error('foo bar'))
thenCallback(promise).then(console.log, console.error) //=> Error: foo bar

// resolved promise
var promise = NativePromise.resolve(123)
thenCallback(promise).then(console.log, console.error) //=> '123'

Related

• always-promise: Promisify, basically, everything. Generator function, callback-style or synchronous function; sync function that returns child process, stream or observable; directly passed promise, stream or child process.
• letta: Let's move to promises! Drop-in replacement for co@4, but on steroids. Accepts sync, async and generator functions.
• native-or-another: Always will expose native Promise if available, otherwise Bluebird but only if you don't give another promise module like q or promise or what you want.
• native-promise: Get native Promise or falsey value if not available.

Contributing

Pull requests and stars are always welcome. For bugs and feature requests, please create an issue.
But before doing anything, please read the CONTRIBUTING.md guidelines.

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