fix arrow keys and local storage

[WardCunningham]

I don't know what I was thinking when I replaced a convoluted switch statement with a malformed table lookup.
This expression has been shown to work.

[paul90]

Could have just reverted to the original, from the decaffeinate script:

    const direction = (() => { switch (event.which) {
      case LEFTARROW: return -1;
      case RIGHTARROW: return +1;
    } })();

[paul90]

This should have been

const dirs = {[LEFTARROW]:-1, [RIGHTARROW]:+1};

[WardCunningham]

Looking a few lines further down I see more complex case analysis and conclude this is really two distinct event handlers struggling to be one.

[WardCunningham]

The return was important because it was an early exit, not because anything of value was being returned. There is a structured-programming rule, single entry with single exit, that would have had us coding that as an if-then-else then no return would have been required. The early exit return should be coded as a separate statement to make it clear that the return is important for control flow.