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A solid, fast Promises/A+ and when() implementation, plus other async goodies.
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when.js

README.md

Promises/A+ logo

Build Status

when.js

When.js is cujoJS's lightweight Promises/A+ and when() implementation that powers the async core of wire.js, cujoJS's IOC Container. It features:

  • A rock solid, battle-tested Promise implementation
  • Resolving, settling, mapping, and reducing arrays of promises
  • Executing tasks in parallel and sequence
  • Transforming Node-style and other callback-based APIs into promise-based APIs

It passes the Promises/A+ Test Suite, is very fast and compact, and has no external dependencies.

What's New?

2.3.0

  • New promise.tap for adding side effects to a promise chain.
  • New MessageChannel scheduler reduces "time-to-first" handler, in environments that support it.
  • Performance optimizations for promise resolution.
  • Internal architecture improvements to pave the way for when.js 3.0.0.

2.2.1

  • Fix for when.defer().reject() bypassing the unhandled rejection monitor. (#166)
  • Fix for when/function, when/callbacks, and when/node/function not preserving thisArg. (#162)
  • Doc clarifications for promise.yield. (#164)

2.2.0

  • New experimental promise monitoring and debugging via when/monitor/console.
  • New when.promise(resolver) promise creation API. A lighter alternative to the heavier when.defer()
  • New bindCallback and liftCallback in when/node/function for more integration options with node-style callbacks.

2.1.1

  • Quote internal usages of promise.yield to workaround .NET minifier tools that don't yet understand ES5 identifier-as-property rules. See #157

2.1.0

  • New when.settle that settles an array of promises
  • New when/guard generalized concurrency guarding and limiting
  • New promise.inspect for synchronously getting a snapshot of a promise's state at a particular instant.
  • Significant performance improvements when resolving promises with non-primitives (e.g. with Arrays, Objects, etc.)
  • Experimental vert.x support
  • DEPRECATED: onFulfilled, onRejected, onProgress handler arguments to when.all, when.any, when.some. Use the returned promise's then() (or otherwise(), ensure(), etc) to register handlers instead.
    • For example, do this: when.all(array).then(onFulfilled, onRejected) instead of this: when.all(array, onFulfilled, onRejected). The functionality is equivalent.

2.0.1

  • Account for the fact that Mocha creates a global named process. Thanks Narsul

2.0.0

  • Fully asynchronous resolutions.
  • Promises/A+ compliance.
  • New when/keys module with all() and map() for object keys/values.
  • New promise.ensure as a better, and safer, replacement for promise.always. See discussion as to why promise.always is mistake-prone.
    • DEPRECATED: promise.always
  • lift() is now the preferred name for what was bind() in when/function, when/node/function, and when/callbacks.
    • DEPRECATED: bind() in when/function, when/node/function, and when/callbacks. Use lift() instead.

Full Changelog

Docs & Examples

API docs

More info on the wiki

Examples

Quick Start

AMD

  1. Get it
    • bower install when or yeoman install when, or
    • git clone https://github.com/cujojs/when or git submodule add https://github.com/cujojs/when
  2. Configure your loader with a package:

    packages: [
        { name: 'when', location: 'path/to/when/', main: 'when' },
        // ... other packages ...
    ]
  3. define(['when', ...], function(when, ...) { ... }); or require(['when', ...], function(when, ...) { ... });

Node

  1. npm install when
  2. var when = require('when');

RingoJS

  1. ringo-admin install cujojs/when
  2. var when = require('when');

Legacy environments

  1. git clone https://github.com/cujojs/when or git submodule add https://github.com/cujojs/when
  2. Add a transient define shim, and a <script> element for when.js

    <script>
        window.define = function(factory) {
            try{ delete window.define; } catch(e){ window.define = void 0; } // IE
            window.when = factory();
        };
        window.define.amd = {};
    </script>
    <script src="path/to/when/when.js"></script>
  3. when will be available as window.when

Running the Unit Tests

Node

Note that when.js includes the Promises/A+ Test Suite. Running unit tests in Node will run both when.js's own test suite, and the Promises/A+ Test Suite.

  1. npm install
  2. npm test

Browsers

  1. npm install
  2. npm start - starts buster server & prints a url
  3. Point browsers at /capture, e.g. localhost:1111/capture
  4. npm run-script test-browser

References

Much of this code was inspired by the async innards of wire.js, and has been influenced by the great work in Q, Dojo's Deferred, and uber.js.

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