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Comment by jiangmy | Hacker News Reader

The difficulty comes from how dynamic language features you support & how accurate the type is inferred. Both in typescript and flow, you need to write annotations/comments to help the compiler perform well.

ESInfer is doing it all statically and without additional stuff needed. You can try it out on the playground section at the bottom of the homepage. Would be glad if there is any feedback :)

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> you need to write annotations/comments to help the compiler perform well.

That's not true of either AFAIK. Annotations help, but it can still catch things without them like:

   function x() { return "x"; }
   x() - 15; // Cannot perform arithmetic operation because string [1] is not a number.

> Both in typescript and flow, you need to write annotations to help the compiler perform well.

For Flow, that's true only in the most literal sense. Flow has excellent inference and can get a lot done without the user writing any annotations.

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