relike

Simple promisify async or sync function with sane defaults. Lower level than promisify thing. Can be used to create promisify method.

You might also be interested in hybridify, hybridify-all, relike-all, letta

Install

npm i relike --save

Usage

For more use-cases see the tests

const relike = require('relike')

Note: It treat functions as asynchronous, based on is-async-function.

Why you should be aware of that? Because if you give async function which don't have last argument called with some of the common-callback-names it will treat that function as synchronous and things may not work as expected.

It's not a problem for most of the cases and for node's native packages, because that's a convention. So, the relike-all package successfuly can promisifies all of the fs functions for example, except fs.createReadStream and fs.createWriteStream which is normal.

relike

Runs fn in native Promise if available, or another provided in relike.Promise. If not given and not support for native Promise, it will use bluebird promise, but only on that enviroments that don't have support.

Params

• <fn> {Function}: Some async or synchronous function.
• [...args] {Mixed}: Any number of any type of arguments, they are passed to fn.
• returns {Promise}: Always native Promise if supported on enviroment.

Example

const fs = require('fs')
const request = require('request')
const relike = require('relike')

relike(fs.readFile, 'package.json', 'utf-8').then(data => {
  console.log(JSON.parse(data).name) // => 'relike'
})

// handles multiple arguments by default (comes from `request`)
relike(request, 'http://www.tunnckocore.tk/').then(result => {
  const [httpResponse, body] = result
})

.promisify

Thin wrapper function around relike(). It accepts a function and returns a function, which when is invoked returns a Promise. Just like any other .promisify method, for example Bluebird.promisify.

Params

• fn {Function}: Some sync or async function to promisify.
• [Promize] {Function}: Promise constructor to be used on enviroment where no support for native.
• returns {Function}: Promisified function, which always return a Promise.

Example

var fs = require('fs')
var relike = require('relike')
var readFile = relike.promisify(fs.readFile)

readFile('package.json', 'utf8')
  .then(JSON.parse)
  .then(data => {
    console.log(data.name) // => 'relike'
  })

// also can promisify sync function
var statFile = relike.promisify(fs.statSync)
statFile('package.json')
  .then(function (stats) {
    console.log(stats.mtime)
  })

.Promise

While relike always trying to use native Promise if available in the enviroment, you can give a Promise constructor to be used on enviroment where there's no support - for example, old broswers or node's 0.10 version. By default, relike will use and include bluebird on old enviroments, as it is the fastest implementation of Promises. So, you are able to give Promise constructor, but it won't be used in modern enviroments - it always will use native Promise, you can't trick that. You can't give custom promise implementation to be used in any enviroment.

Example

var fs = require('fs')
var relike = require('relike')

relike.promisify.Promise = require('q') // using `Q` promise on node 0.10
var readFile = relike.promisify(fs.readFile)

readFile('package.json', 'utf8')
  .then(console.log, console.error)

One way to pass a custom Promise constructor is as shown above. But the other way is passing it to .Promise of the promisified function, like that

var fs = require('fs')
var relike = require('relike')
var statFile = relike.promisify(fs.stat)

statFile.Promise = require('when') // using `when` promise on node 0.10
statFile('package.json').then(console.log, console.error)

One more thing, is that you can access the used Promise and can detect what promise is used. It is easy, just as promise.Promise and you'll get it. Or look for promise.___bluebirdPromise and promise.___customPromise properties. .___bluebirdPromise (yea, with three underscores in front) will be true if enviroment is old and you didn't provide promise constructor to .Promise.
So, when you give constructor .__customPromise will be true and .___bluebirdPromise will be false.

var fs = require('fs')
var relike = require('relike')

var promise = relike(fs.readFile, 'package.json', 'utf8')
promise.then(JSON.parse).then(function (val) {
  console.log(val.name) // => 'relike'
}, console.error)

console.log(promise.Promise) // => used Promise constructor
console.log(promise.___bluebirdPromise) // => `true` on old env, falsey otherwise
console.log(promise.___customPromise) // => `true` when pass `.Promise`, falsey otherwise

Or finally, you can pass Promise constructor as second argument to .promisify method. Like that

const fs = require('fs')
const relike = require('relike')
const readFile = relike.promisify(fs.readFile, require('when'))

const promise = readFile('index.js')

console.log(promise.Promise) // => The `when` promise constructor, on old enviroments
console.log(promise.___customPromise) // => `true` on old environments

Related

• callback2stream: Transform sync, async or generator function to Stream. Correctly handle errors. homepage
• hybridify: Create sync or async function to support both promise and callback-style APIs… more | homepage
• letta: Promisify sync, async or generator function, using relike. Kind of promisify, but… more | homepage
• limon: The pluggable JavaScript lexer. Limon = Lemon. | homepage
• promise2stream: Transform ES2015 Promise to Stream - specifically, Transform Stream using… more | homepage
• relike-all: Promisify all functions in an object, using relike. | homepage
• use-ware: Adds sync plugin support to your application. Kinda fork of use -… more | homepage
• use: Easily add plugin support to your node.js application. | homepage
• value2stream: Transform any value to stream. Create a stream from any value -… more | homepage

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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