Compared to asm.js today it'll start-up faster because the format parses quicker. It will also be smaller in size compared to a gzipped asm.js equivalent. Edit

Compared to asm.js today it'll start-up faster because the format parses quicker. It will also be smaller in size compared to a gzipped asm.js equivalent. Edit: Also, browser vendors will optimize it more consistently than they do with asm.js currently. Also, compared to Emscripten the llvm backend for WebAssembly is upstream so you might see more frontend languages like Swift and Rust add support for it.