1module.exports = function (xs, fn) { 2 var res = []; 3 for (var i = 0; i < xs.length; i++) { 4 var x = fn(xs[i], i); 5 if (isArray(x)) res.push.apply(res, x); 6 else res.push(x); 7 } 8 return res; 9}; 10 11var isArray = Array.isArray || function (xs) { 12 return Object.prototype.toString.call(xs) === '[object Array]'; 13}; 14