I guess the point is that with Babel you can enable so called "stage 0" language features, which aren't in the spec yet but someone has created a Babel plugin f

I guess the point is that with Babel you can enable so called "stage 0" language features, which aren't in the spec yet but someone has created a Babel plugin for (e.g. decorators). With Typescript, you can't do this, because the code has to pass through the Typescript compiler first, which doesn't support (most of) these features (e.g. it does support decorators IIRC) so will throw an error when it finds an unfamiliar language construct, and it doesn't have a plugin architecture like Babel, so you can't add them in that way. One example is the spread/rest syntax which is sometimes used in React projects isn't fully supported in TS: https://github.com/Microsoft/TypeScript/issues/2103 https://github.com/Microsoft/TypeScript/issues/2103. I should point out you can use Babel and Typescript, so the Babel processes the output from tsc (needed for using e.g. async/await at present, as tsc can't compile these down to ES5), but tsc has to run first to make the code into valid JS (on this note, I was surprised how easy it was to remove TS from a project - Babel will ignore most of the TS specific stuff such as interface and type declarations, as it already strips them out for Flow compatibility and the syntax is largely the same)