promise-defer

PromiseDefer.js

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PromiseDefer.js is a small Promise.defer "polyfill" to create a Deferred object you can later resolve or reject and get a Promise out of. It used to exist in browsers and JavaScript engines as Promise.defer, but was later deprecated. It's still useful in some cases.

PromiseDefer.js uses the native ES6 Promise by default, but you can pass it another Promises/A+ compatible constructor function.

Installing

npm install promise-defer

PromiseDefer.js follows semantic versioning, so feel free to depend on its major version with something like >= 1.0.0 < 2 (a.k.a ^1.0.0).

Using

var defer = require("promise-defer")

var deferred = defer()
deferred.resolve(42)
deferred.promise // Will eventually be resolved with 42.

var rejection = defer()
rejection.reject(new Error("I'll have none of that, thank you."))
rejection.promise // Will eventually be rejected with the error.

PromiseDefer.js will use the global ES6 Promise constructor by default that's starting to become available in browsers and JavaScript runtimes (e.g. the V8 in Node.js v0.11). It doesn't therefore have any outside dependencies.

Using another Promise implementation

If you'd like to use another promise implementation or are running in an environment that doesn't have the native Promise, pass a Promises/A+ compatible constructor as the first argument:

var Bluebird = require("bluebird")
var defer = require("promise-defer").bind(null, Bluebird)
defer().promise // => An instance of Bluebird.

Deferred class

If you need to programmatically differentiate beteween regular objects and Deferred instances, use the instanceof operator:

var Deferred = require("promise-defer")
Deferred() instanceof Deferred // => true

License

PromiseDefer.js is released under a Lesser GNU Affero General Public License, which in summary means:

• You can use this program for no cost.
• You can use this program for both personal and commercial reasons.
• You do not have to share your own program's code which uses this program.
• You have to share modifications (e.g. bug-fixes) you've made to this program.

For more convoluted language, see the LICENSE file.

About

Andri Möll typed this and the code.
Monday Calendar supported the engineering work.

If you find PromiseDefer.js needs improving, please don't hesitate to type to me now at andri@dot.ee or create an issue online.