I couldn't tell from your wording if you knew this already, but we wrote a JS->TS converter too. I didn't call it out very clearly but it's the second to last link in the post.
I am really sad that TypeScript gave up on their spec. It previously was one of the strengths of the language that I was happy to cite. I guess it's a common crutch for languages (Python and so on) to say "the implementation is the spec" but without a spec to guide you, you lose sight of which features are intentional or accidents or even what the distinction between the two are.
The Closure library does has some great stuff in it. It's the accumulation of years of experience of working around lots of really subtle issues in lot of browsers. On the other side it also has a lot of code for issues that are obsolete, and it's hard to know which pieces are for what.
I am really sad that TypeScript gave up on their spec. It previously was one of the strengths of the language that I was happy to cite. I guess it's a common crutch for languages (Python and so on) to say "the implementation is the spec" but without a spec to guide you, you lose sight of which features are intentional or accidents or even what the distinction between the two are.
The Closure library does has some great stuff in it. It's the accumulation of years of experience of working around lots of really subtle issues in lot of browsers. On the other side it also has a lot of code for issues that are obsolete, and it's hard to know which pieces are for what.