This is just a temporary limitation of asm.js because it has no access to garbage-collected data. In the future it should have support for managed languages.
> Q. Can asm.js serve as a VM for managed languages, like the JVM or CLR?
A. Right now, asm.js has no direct access to garbage-collected data; an asm.js program can only interact indirectly with external data via numeric handles. In future versions we intend to introduce garbage collection and structured data based on the ES6 structured binary data API, which will make asm.js an even better target for managed languages. [1]