Right, sorry I think I wasn't clear. I'm wondering how one goes about something like this

    as.map(a =>
      <tr>{
        bs.map(b => <td onClick={() => foo(a, b)}></td>)
      }</tr>
    )

Notice how both `a` and `b` are passed into `foo`. There are other possible permutations, such as passing indices or properties of items. I believe it's possible to access `b.bar` easily enough, but it wasn't clear how to access `a` or the index of `as.map` from inside the inner loop.