Flatten array with promises

flatten.js

module.exports = function(array) {
	return array.reduce(function(total, subArray) {
		subArray.forEach(function(item) {
			total.push(item);
		});
		
		return total;
	}, []);
}

usage.js

var flatten = require("./flatten");

doThing().map(function(item){
	...
}).then(flatten).then(function(flattenedArray) {
	...
});