Asm.js and WebAssembly are meant for C++ or languages in which the memory management is manual. Garbage collected languages don't work, unless you implement the GC in asm.js as well. And at that point it's far better to compile that language to plain Javascript.
Also, I hate the "transpiling" verb and your usage of it is incorrect. We started using "to transpile" as a way to inform people that some compilers, such as CoffeeScript, have a Javascript output that's still readable and that doesn't lose abstraction in the process, the "transpiler" being defined as a "source to source compiler". People preferred this term to convey the information that some languages like CoffeeScript are just mere syntactic sugar over Javascript.
On one hand that's superfluous when the very definition of a "compiler" is that of a program that transforms source code from one programming language to another. And on the other hand, people are using it incorrectly. The minified output of something like Google's Closure compiler, coupled with the higher-level abstractions in languages like ClojureScript or Scala.js, etc, leads to a Javascript output that is no longer readable and that does lose abstraction in the process.