Optimizations

Building arrays via `arr[i] = x` is ~45% faster than `arr.push(x)`. See http://jsperf.com/sylvesterloops/2
Store references to mOrV.elements.
Inline loops instead of call out to map, which calls to forEach.
You know the length already in a lot these cases, you should use `new Array(n)` and then set the indexs `x[i] = <val>`