[WorldMaker]

> 2. Pre-1.5 TypeScript had something called "internal modules" which were renamed to "namespaces" and are generally discouraged now. Hopefully your code is not using that feature.

Related to this, the TypeScript pre-1.0 import/export syntax for "external modules" was grandfathered in, but the semantics changed alongside the "internal modules" changes in 1.5. So pre-1.0 import/exports still mostly "compile" in post-1.5, but have very different semantics and that can often cause a lot of downstream module shape headaches, depending (and exacerbated by) the module format you are targeting.

A first pass making sure to rewrite all import/require/export statements can save you a lot of work later, even though it won't directly cause compile errors. You can get some compile errors by making sure you try to compile to a "proper" post-ES2015 module format (--module esm or --module es2015 or --module esnext even). There's also tslint rules such as "no-import-requires".