WebAssembly has no way of directly interacting with the DOM. It has to use JS interopt which is quite slow. It'll take a couple years to get Wasm up to speed. I

WebAssembly has no way of directly interacting with the DOM. It has to use JS interopt which is quite slow. It'll take a couple years to get Wasm up to speed. It'll be a couple more years to add the rest of the low-level interfaces and even more time to deliberate about a GC spec (you don't want to ship apps with entire language environments attached). It'll be a couple more years to deliberate over new DOM APIs and a couple more to implement them. After that, it'll be a half-decade or more until old browser share drops low enough to use it without needing a JS equivalent.