I responded to someone else saying this, but I guess it bears repeating. I'm not saying its a free lunch - it is a build step - there are things to learn - some of the more esoteric types can be very hard to understand. I exaggerated when I said there was no downsides, what I mean to say is that in the cost benefit analysis as I see it so far, the benefits massively outweigh the costs. I've written a fair bit of TS so far and I find it hard to imagine writing a significant side code base without it in JS-land.

I'm not blinded by the hype, im here asking people for what they see as the downsides, the reasons they may have or have heard of why teams didn't pick TS (or better yet did and had some reason it didn't work out).