alt Hacker NewsAssuming we’re talking about TypeScript here, because JavaScript doesn’t have exportable types… Any instance in JavaScript, whether or not its type is exported, is just an object like any other, that any other module is free to enumerate and mess with once it receives it. In Ada there are no operations on an instance of a private type except the ones provided by the source module.
In other words, if module X returns a value x of unexported type T to module Y, code in module Y is free to do x.foo = 42.
* only if `x` is _an object_ (read: has methods)
To preempt the obvious: yes, I know _everything_ (nearly) in JavaScript is an object, but a module exporting a `Function` can expect the caller to use the function, not enumerate it for methods. And the function can use a declaration in the module that wasn't exported, with the caller none the wiser about it.