Unfortunately, my ChromeBook doesn’t like PPAs for installing newer versions of Node.js than are part of Debian. If there’s a cheat-sheet on how to work around this, please tell me.
Anyway, adding -DNODE_JS_EXECUTABLE=$(type -p node) to the configure script seems to have fixed things. I’ve updated the SWI-Prolog in the browser using WASM page, but I’ve noticed that there’s also Building SWI-Prolog using Emscripten for WebAssembly (WASM) … should the latter also be updated, or is it obsolete?