We eventually may want dart2wasm to actually work in non-JavaScript environments (wasmtime, wasmer, etc). @askeksa had mentioned a list of a few things that would definitly need to be addressed in order to remove the dependency on a JS/browser environment:

We are currently dependent on JS for the following components:

• Event loop
• Printing
• OS-level timer features, such as current time
• Weak maps, weak references, finalizers
• Stack traces
• Conversions between double and String
• Regexps
• Math functions (sin, pow, exp, etc.)

For each of these, we'll have to either:

• (1) implement the feature in Dart (or intrinsically in the compiler),
• (2) link to an implementation compiled to Wasm, or
• (3) import an external implementation from the host.