Unbreakable is a JavaScript Promise library that implements the JavaScript 2015 (ES6) Promises API and conforms to the Promises/A+ specification. It differentiates itself from other promise implementations by fully-encapsulating the state of promise objects.

The other promise implementations I looked at allow you to do something like this:

var promise = new Promise(function(resolve, reject) {
  // ...
});

promise._state = 'resolved';
promise._resolveValue = 'foo';

promise.then(function(value) {
  console.log(value); // foo
});

While I realize most everyone knows better than to do this, I wanted to create a promise implementation that makes it impossible for anyone to improperly mess with the state of a promise object. Thus, an Unbreakable promise's state is inaccessible to the outside world and can only be modified via the callbacks provided to its constructor argument as allowed by the promises spec.

npm install --save unbreakable

If you're working on an ES6 project, you can import the ES6 source file directly:

import Promise from 'unbreakable/lib/Unbreakable';

If you're working on a non-ES6 project, you can load Unbreakable as a transpiled UMD module from the dist/ directory.

Refer to MDN's Guide to the ES6 Promise API, as this is the API that Unbreakable implements.

If you wish to contribute to the development of Unbreakable, here are the things to know.

Unbreakable's tests are written with tape.

npm test

npm run spec

npm run build_tests

Then open browser-tests.html in your browser.

npm run build

MIT