Although this is only a handful of lines [0] it's nice to design things well.

- By providing a 'builder' you add a clear API to the struct object's constructor. It doesn't make any more or fewer claims of capibility than it needs to. By exposing the internal storage you break that level of abstraction.

- Even assuming that the JS object type _is_ ordered, the ADT of the Struct type may be subtly different to the ADT of the object. By coupling the two you may prevent future flexibility.

- To that point, the 'field' method _does_ do something with each invocation (forceEndianess) as it adds it to the internal storage. If you passed in a map object it would still need to traverse each key to do that work, which (knowing JS objects) might make it more complicated.

[0] https://github.com/francisrstokes/construct-js/blob/master/s...