This gist demonstrates how you can manage Mock Service Worker handlers in Next.js API Routes style in your Vite project

handlers.ts

import { rest } from "msw";

// https://vitejs.dev/guide/features.html#glob-import
const imports = import.meta.glob("./api/**/*.ts", { eager: true });

export const handlers = Object.entries(imports).reduce(
  (allHandlers, [path, handlers]) => {
    // map "./path/[to]/handlers.js" -> "/api/path/:to/handlers"
    const apiPath =
      "/" +
      path
        // trim "./" at start
        .replace(/^\.\//, "")
        // trim ".js" at end
        .replace(/\.[^/.]+$/, "")
        // replace "[param]" with ":param"
        .replace(/\[([^/]*)\]/g, ":$1");

    Object.getOwnPropertyNames(handlers).forEach((verb) => {
      const handler = handlers[verb];

      const method = verb.toLowerCase();

      // for every method in handlers, register an msw handler
      if (method in rest) {
        allHandlers.push(rest[method as keyof typeof rest](apiPath, handler));
      }
    });

    return allHandlers;
  },
  []
);