Simple promisify async or sync function with sane defaults. Lower level than promisify
thing. Can be used to create promisify
method.
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.
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(request, 'http://www.tunnckocore.tk/').then(result => {
const [httpResponse, body] = result
})
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)
})
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')
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')
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)
}, console.error)
console.log(promise.Promise)
console.log(promise.___bluebirdPromise)
console.log(promise.___customPromise)
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)
console.log(promise.___customPromise)
Related
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.