Vite Plugin: emit an asset using `emitFile` and `configureServer`

plugin.ts

import type { PluginOption } from "vite";

export function plugin(): PluginOption {
  return [
    {
      apply: "serve",
      name: "example-serve",
      configureServer(server) {
        server.middlewares.use("/subfolder/example.txt", (_req, res) => {
          res.appendHeader("Content-Type", "text/plain");
          res.end("Generated by vite dev");
        });
      }
    },
    {
      apply: "build",
      name: "example-build",
      generateBundle() {
        this.emitFile({
          type: "asset",
          fileName: "subfolder/example.txt",
          source: "Generated by vite build",
        });
      }
    }
  ];
}