As always, less complexity and less expressive power at a given level go hand in hand: Deno as it exists right now can’t work even with a relatively tame nonstandard approach to JSX such as that in Solid.js[1] (without essentially running a build step at startup), let alone a full language extension like Svelte[2] (there is a thing for that now[3], but it seems to be squeezing in a build system through a localhost server IIUC?).