Given the following. I want to lazily apply `transform` to each member of the iterable returned from `Object.keys`.

How can I do this?

```
function* numbers(upto, transform) { 
  yield* Object.keys([...Array(upto)]); // How can `transform` be applied here lazily?
}

function timesTwo(n) {
    return n*2;
}

var generator = numbers(31, timesTwo)

for(var i of generator) {
    console.log(i); // 0 2 4 6 8... 60
}

```