I don't know what the usual speed difference of TypeScript programs vs JavaScript
programs.
But the argument that TypeScript generates a JavaScript, so
it must have similar speed doesn't hold in general.
If the compiler in question is a whole-program compiler,
it can make optimizations that a normal person couldn't do.
As an anecdote in [1] a raytracing program were implemented
in both Scheme and C. The Stalin compiler (a whole-program Scheme compiler)
produced an executable 45% faster than the one produced by g++.
The Stalin compiler produced the excecuable by compiling Scheme to C,
and then used a C compiler to produce the final executable.
The price of a whole-program compiler? Well, the compile time are huge.
But the argument that TypeScript generates a JavaScript, so it must have similar speed doesn't hold in general.
If the compiler in question is a whole-program compiler, it can make optimizations that a normal person couldn't do.
As an anecdote in [1] a raytracing program were implemented in both Scheme and C. The Stalin compiler (a whole-program Scheme compiler) produced an executable 45% faster than the one produced by g++. The Stalin compiler produced the excecuable by compiling Scheme to C, and then used a C compiler to produce the final executable.
The price of a whole-program compiler? Well, the compile time are huge.
[1] Scroll to Siskind's comment. https://groups.google.com/g/comp.lang.scheme/c/NJxRsdMNKz4
For those curious about the actual programs and results: https://web.archive.org/web/20071011073406/http://www.ffcons...