3 ms·

That is optional typing. The author is talking about gradual or progressive typing.

• zpr 9y ago
  But he mentions he wishes he could start dynamically and end statically. By enabling Flow at the end, don't you basically achieve that? You can also enable it progressively for files as you move on, and still rapidly prototype without it. In fact, unless I'm mistaken I believe it's "opt-in" by default, ie. Flow won't scan the file unless you include the special comment keyword at the top of the file.
• mercer 9y ago
  Could you explain the difference? I though TypeScript was a good example of gradual typing.