Waterfall on promise

tests.js

waterfall(['a', 'bbbb', 'cc'], function(item){
	return function(resolve){
		setTimeout(function(){
			console.log(item);
			resolve();
		}, item.length * 1000);
	};
});

waterfall.js

function waterfall(items, resolver) {
	items.reduce(function (promise, item) {
		return promise.then(function () {
			return new Promise(resolver(item));
		});
	}, Promise.resolve());
}