Show HN: A simple calculator implemented using the shunting yard algorithm

I like how simple it is. Thanks for sharing.

By the way, I found one or two bugs.

The empty parentheses alone are treated as undefined:

  > ()
  undefined

And I think any equation using empty parentheses as an expression gets treated as NaN:

  > 5 + ()
  NaN

Empty parentheses should probably just be a parse error.