there was a minimal CommonJS promises library with useful things like parallel execution, fulfilments and exception handling, without losing the beautiful simplicity of .then().

Chat with me about andthen right now - I hang out on http://askabt.com/andthen. <shameless-plug> Askabt is like an IRC channel, but prettier, easier and works via the web and your XMPP account. Sign in with your Github account to join the communities around your repos and the languages you use. </shameless-plug>

Parallel execution is like saying, "Do this and that, then do the other thing." With andthen, you can express it like:

	doThis().and(doThat()).then(function(thisResult, thatResult) {
		return doOther();
	});

Exceptions thrown in a .then() callback are caught and turned into promise rejections so they can be handled by subsequent errback's.

	promise.then(function() {
		throw new Error('Boo!');
	}).then(null, function(err) {    // Passing an error callback.
		console.log(err.message);    // Boo!
	});

If there's a chain of promises where you forgot to add an error callback, andthen will turn promise rejections into errors that are then thrown. This will alert you to problems that, with other libraries, might go undetected.

If you want to use it in Node.js

npm install and-then

To use on the client side, just download andthen.js (or andthen.min.js) from Github.

Include andthen using CommonJS require(), AMD require, or simple <script> tags. Usage is pretty close to other deferred libraries:

	function promiseMaker() {
		var result = andthen();
		
	}

Call .and() on Promise A and pass it a Promise B to obtain a new promise C. When both A and B have returned, promise C will resolve into both values, i.e. a .then() callback attached on C will be called with two arguments.

You can chain .and()'s. The resolution values of both A and B are passed as arguments to the .then() callback on promise C. For example:

	getA().and(getB()).then(function(a, b) {
		// ...
	});
	
	getA().and(getB()).and(getC()).then(function(a, b, c) {
		// ...
	});

Sometimes you want a promise that's already resolved - for example you need to pass it to a function that expects a promise. You can save some keystrokes using the andthen(value) syntax.

You can also pre-fulfil the multi-valued promises that .and() generates, like andthen(val1, val2, val3).

Loosely based on the documentation of kriskowal's q library.

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