Any Promise
Let your library support any ES 2015 (ES6) compatible Promise
and leave the choice to application authors. The application can optionally register its preferred Promise
implementation and it will be exported when requiring any-promise
from library code.
If no preference is registered, defaults to the global Promise
for newer Node.js versions. The browser version defaults to the window Promise
, so polyfill or register as necessary.
Usage with global Promise:
Assuming the global Promise
is the desired implementation:
$ npm install mz
The installed libraries will use global Promise by default.
var Promise = require('any-promise')
function promiseReturningFunction(){
return new Promise(function(resolve, reject){...})
}
Usage with registration:
Assuming bluebird
is the desired Promise implementation:
$ npm install bluebird
$ npm install any-promise
$ npm install mz
Register your preference in the application entry point before any other require
of packages that load any-promise
:
require('any-promise/register/bluebird')
require('any-promise/register')('bluebird', {Promise: require('bluebird')})
Now that the implementation is registered, you can use any package depending on any-promise
:
var fsp = require('mz/fs')
var Promise = require('any-promise')
It is safe to call register
multiple times, but it must always be with the same implementation.
Again, registration is optional. It should only be called by the application user if overriding the global Promise
implementation is desired.
Optional Application Registration
As an application author, you can optionally register a preferred Promise
implementation on application startup (before any call to require('any-promise')
:
You must register your preference before any call to require('any-promise')
(by you or required packages), and only one implementation can be registered. Typically, this registration would occur at the top of the application entry point.
Registration shortcuts
If you are using a known Promise
implementation, you can register your preference with a shortcut:
require('any-promise/register/bluebird')
import 'any-promise/register/q';
Shortcut registration is the preferred registration method as it works in the browser and Node.js. It is also convenient for using with import
and many test runners, that offer a --require
flag:
$ ava --require=any-promise/register/bluebird test.js
Current known implementations include bluebird
, q
, when
, rsvp
, es6-promise
, promise
, native-promise-only
, pinkie
, vow
and lie
. If you are not using a known implementation, you can use another registration method described below.
Basic Registration
As an alternative to registration shortcuts, you can call the register
function with the preferred Promise
implementation. The benefit of this approach is that a Promise
library can be required by name without being a known implementation. This approach does NOT work in the browser. To use any-promise
in the browser use either registration shortcuts or specify the Promise
constructor using advanced registration (see below).
require('any-promise/register')('when')
This registration method will try to detect the Promise
constructor from requiring the specified implementation. If you would like to specify your own constructor, see advanced registration.
Advanced Registration
To use the browser version, you should either install a polyfill or explicitly register the Promise
constructor:
require('any-promise/register')('bluebird', {Promise: require('bluebird')})
This could also be used for registering a custom Promise
implementation or subclass.
Your preference will be registered globally, allowing a single registration even if multiple versions of any-promise
are installed in the NPM dependency tree or are using multiple bundled JavaScript files in the browser. You can bypass this global registration in options:
require('../register')('es6-promise', {Promise: require('es6-promise').Promise, global: false})
Library Usage
To use any Promise
constructor, simply require it:
var Promise = require('any-promise');
return Promise
.all([xf, f, init, coll])
.then(fn);
return new Promise(function(resolve, reject){
try {
resolve(item);
} catch(e){
reject(e);
}
});
Except noted below, libraries using any-promise
should only use documented functions as there is no guarantee which implementation will be chosen by the application author. Libraries should never call register
, only the application user should call if desired.
Advanced Library Usage
If your library needs to branch code based on the registered implementation, you can retrieve it using var impl = require('any-promise/implementation')
, where impl
will be the package name ("bluebird"
, "when"
, etc.) if registered, "global.Promise"
if using the global version on Node.js, or "window.Promise"
if using the browser version. You should always include a default case, as there is no guarantee what package may be registered.
Support for old Node.js versions
Node.js versions prior to v0.12
may have contained buggy versions of the global Promise
. For this reason, the global Promise
is not loaded automatically for these old versions. If using any-promise
in Node.js versions versions <= v0.12
, the user should register a desired implementation.
If an implementation is not registered, any-promise
will attempt to discover an installed Promise
implementation. If no implementation can be found, an error will be thrown on require('any-promise')
. While the auto-discovery usually avoids errors, it is non-deterministic. It is recommended that the user always register a preferred implementation for older Node.js versions.
This auto-discovery is only available for Node.jS versions prior to v0.12
. Any newer versions will always default to the global Promise
implementation.
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