AI solution for JavaScript Coding Question on BFE.dev
54. flatten Thunk

Here's one possible solution to the "flattenThunk" problem:

function flattenThunk(thunk) {
  return function(callback) {
    thunk(function(error, result) {
      if (error) {
        callback(error);
      } else if (typeof result === 'function') {
        flattenThunk(result)(callback);
      } else {
        callback(null, result);
      }
    });
  };
}

This flattenThunk function returns a new thunk that takes a callback function as its argument. It then calls the original thunk, passing in a new callback function. This new callback function checks if an error occurred or if the result is a function (i.e. a thunk), in which case it recursively calls flattenThunk on the result and passes in the original callback. If there is no error and the result is not a function, it passes the result to the original callback.

With the above code, you can now call flattenThunk(func3) and pass in a callback function that will receive the final result (in this case, 'ok') or any error that occurred along the way.