It's a format designed to be a target for static languages that do manual memory management (like C/C++) instead of JavaScript that some engines know how to rec

It's a format designed to be a target for static languages that do manual memory management (like C/C++) instead of JavaScript that some engines know how to recognize and optimize. The binaries are smaller and much faster to parse and the sandbox model results in much less overhead. For a concrete example, at least two JavaScript engines (those of Chrome and Firefox) need to emit almost no range checks on regular memory accesses with WebAssembly on 64-bit computers. (For those interested in going past ELI5, they do this by allocating a large chunk of virtual address space, such that any out of range pointers will land somewhere in that space (WebAssembly currently only has 32-bit pointers). Some of the space is filled with memory, and the rest causes a controlled signal/exception so the engine can safely terminate the instance.)