Simplified find left-most fulfilled

find-first.js

function findFirst(promises){
	return recurseFindFirst(0, [], promises);
}

function recurseFindFirst(i, errors, promises) {
	if(i === promises.length) {
		var e = new Error('All promises rejected');
		e.errors = errors;
		return when.reject(e);
	}

	return when(promises[i]).catch(function(e) {
		errors.push(e);
		return recurseFindFirst(i+1, errors, promises);
	});
}

var testList = [
	when.reject(new Error('a')),
	when.reject(new Error('b')),
	when.resolve('c'),
	when.reject(new Error('d'))
];

findFirst(testList).done(console.log.bind(console));