Doesn't TypeScript – as mentioned above – solve all JavaScript type problems? I have, in 6 years, never encountered a single type error originating from a TS file.
Biggest problems with TypeScript IMO are that it’s a layer rather than a language proper and that untyped JS problems can too easily worm their way in if you’re using any libraries at all. Also depending on the group of developers involved, the ease at which one can pull the escape hatch and opt out of TS is a liability and can render much of its benefit moot.