Edge / Workers

@lumis-sh/lumis runs on edge and worker hosts with the same API as Node and browsers. Install it with the parser packages for the languages you highlight:

npm install @lumis-sh/lumis @lumis-sh/themes @lumis-sh/wasm-rust

Tested on Supabase Edge Functions, Cloudflare Workers, and Vercel on both the Node.js runtime with Fluid compute and the Edge runtime.

// supabase/functions/highlight/index.ts
import { createHighlighter } from "npm:@lumis-sh/lumis";
import { htmlInline } from "npm:@lumis-sh/lumis/formatters";
import dracula from "npm:@lumis-sh/themes/dracula";
import rust from "npm:@lumis-sh/wasm-rust";

const highlighter = createHighlighter({ languages: [rust] });

Deno.serve(async (req) => {
  const { code } = await req.json();
  const hl = await highlighter;
  const html = hl.highlight(code, htmlInline({ language: rust, theme: dracula }));
  return Response.json({ html });
});

npx supabase functions deploy highlight

How it works

Cloudflare Workers and Vercel's Edge runtime cannot compile WebAssembly while a request runs, only modules their build step compiled at deploy time. Under the workerd export condition, which Wrangler selects, and the edge-light condition, which Next.js selects for the Edge runtime, Lumis and every @lumis-sh/wasm-* package import their .wasm files as modules. It follows that, on those two hosts:

• every language highlighted there, injected ones included, has to come from a package the code imports
• a resolver cannot work, because the parser bytes it fetches could not be compiled
• a parser you supply yourself must be a WebAssembly.Module, such as import parser from "./tree-sitter-rust.wasm" on Workers or "./tree-sitter-rust.wasm?module" on Vercel, not bytes or a URL

Supabase Edge Functions, Deno and Vercel's Node.js runtime compile WebAssembly at run time, so none of this applies there.

On edge hosts runtimeKind() returns 'wasm'. Workers stops the clock while a request runs, so timing a highlight with performance.now() there reports 0.

Other hosts

Another edge host works when it does one of these:

• compiles WebAssembly from bytes at run time, as Deno does; the ordinary entries work there
• imports .wasm files as compiled modules and resolves the workerd or edge-light export condition, as Wrangler and Next.js do

A host that does neither cannot run Lumis.

See JavaScript / TypeScript for the rest of the API.