Creates a lazy promise that only starts its work once there is interest in the outcome

lazyPromise.js

var when = require('when'),
    whenFn = require('when/function');

function lazyPromise(work) {
	var defer, started, resolver, promise, then;

	defer = when.defer();
	started = false;

	resolver = defer.resolver;
	promise = defer.promise;
	then = promise.then;

	promise.then = function () {
		if (!started) {
			started = true;
			whenFn.apply(work).then(resolver.resolve, resolver.reject);
		}
		return then.apply(promise, arguments);
	};

	return promise;
}