module.exports = function (xs, fn) { var res = []; for (var i = 0; i < xs.length; i++) { var x = fn(xs[i], i); if (isArray(x)) res.push.apply(res, x); else res.push(x); } return res; }; var isArray = Array.isArray || function (xs) { return Object.prototype.toString.call(xs) === '[object Array]'; };