My surprise is typescipt is so slow. I have never used it yet, but I think will never too.
I have used its it came out so I do know what it is, but I have people ask if they should write their new program in TypeScript, thinking this is something they can write it in and then run it.
My usage of it is limited to JavaScript, so I see it as adding a static typing layer to JavaScript, so that development is easier and more logical, and this typing information is stripped out when transpiled, resulting in pure JavaScript which is all the browser understands.
The industry calls it a programming language, so I do too just because this is not some semantic battle I want to get into. But in my mind it's not.
There's probably a word for what it is, I just can't think of it.
Type system?
And I don't understand a "10x speedup" on TypeScript, because it doesn't execute.
I can understand language services for things like VS Code that handle the TypeScript types getting 10x faster, but not TypeScript itself. I assume that is what they are talking about in most cases. But if this logic isn't right, let me know.
Theoretically(!) using TS over JS may indirectly result in slightly better perf though because it nudges you towards not mutating the shape of runtime objects (which may cause the JS engine to re-JIT your code). The extra compilation step might also allow to do some source-level optimizations, like constant folding. But I think TS doesn't do this (other JS minifiers/optimizers do though).
Languages like Python and Ruby are much much slower than that (CPython is easily 10x slower than V8) and people don't seem to care.
Typescript's sweet spot is making existing Javascript codebases more manageable.
It can also be fine in I/O-heavy scenarios where Javascript's async model allows it to perform well despite not having the raw execution performance of lower-level languages.