The delta between TypeScript and the JS standard is very small (for many TS users I expect it's a trivia challenge that they won't be able to answer: "write a T

The delta between TypeScript and the JS standard is very small (for many TS users I expect it's a trivia challenge that they won't be able to answer: "write a TS program that isn't valid JS once you erase the types"). As you yourself point out, you were using features that weren't in a browser and needed a different transpiler to implement them. I think object spread still isn't even part of the standard(?) and you could imagine the standard diverging from the babel implementation of it, so the risk is mostly the same there. The TypeScript team is pretty committed to tracking the standard, and e.g. turn down feature proposals that aren't far enough along in the standards process. See https://github.com/Microsoft/TypeScript/issues/16 https://github.com/Microsoft/TypeScript/issues/16 for a feature users are begging for that they aren't implementing. Another good example is that they had their own module system which they deprecated in favor of the ES6 module system. [disclaimer: big TS fan; I think Flow is fine too but I don't think it offers any advantage with respect to the issues you're concerned about here]