mapconcat Returns the result of applying concat to the result of applying a function to values. Install npm i -S mapconcat Usage var assert = require('assert');var mapconcat = require('mapconcat'); function reverse(arr) { return arr.reduce(function(acc, val, idx) { return acc.concat(arr[arr.length - idx - 1]); }, []);} var a = [3, 2, 1];var b = [6, 5, 4];var arr = mapconcat([a, b], reverse);assert.deepEqual(arr, [1, 2, 3, 4, 5, 6]); // true