There are now builtin iterator versions of most of these looped functions [1], should be shipping in stable Chrome next month. The "give me an array at the end" function is spelled toArray.
But it's not going to help all that much with this problem. The iterator protocol in JS involves an allocation for every individual value, and while in some cases that can be optimized out, it's pretty tricky to completely optimize.
It's always going to be difficult to beat a c-style for loop for performance.
Lodash is MUCH faster than native because it uses iterators so you aren't actually looping over and over.
We need builtin iterator versions of all these looped functions so it adds an implicit/explicit `.valueOf()` that calls the chain and allocates only one new array.