I’m happy to report that we at Mozilla have started working with Chromium, Edge and WebKit engineers on creating a new standard, WebAssembly, that defines a portable, size- and load-time-efficient format and execution model specifically designed to serve as a compilation target for the Web. As reflected in the high-level goals, a central requirement for WebAssembly is that it integrate well with the rest of the Web platform and that the initial version run efficiently on current browsers using a client-side polyfill. As demonstrated, the polyfill can leverage asm.js to get great performance. For existing Emscripten/asm.js users, targeting WebAssembly will be as easy as flipping a flag. Thus, it is natural to view WebAssembly as the next evolutionary step of asm.js (a step many have requested and anticipated).
We’re pretty early into the overall process—there is no draft spec or even final formal standards body chosen, just a W3C Community Group, some initial prototyping and early cross-browser consensus on the high-level design documents. Going forward, there will be a lot more iteration and experimentation under the WebAssembly GitHub organization. For questions, check out the still-emerging FAQ. Brendan Eich also has a vibrant blog post with more context, history and JS perspective.