Move Express middleware to separate modules - node.js

Question

I have lots of app.use(...) in my express app, and they get messy and complex and there's config all over the place. So I want to move them to separate modules so they're easier to test.
So I have this Middleware.ts base class for my middleware wrappers:
export default abstract class Middleware {
public run(): express.RequestHandler {
try {
return this.runImpl;
}
catch (err) {
log("Failed to init middleware " + err);
throw err;
}
}
public abstract runImpl(): express.RequestHandler;
}
And a subclass, e.g. StaticMiddleware.ts for serving static files:
export class StaticMiddleware extends Middleware {
public runImp(): express.RequestHandler {
// this is a simple example, but most middleware are more
// complicated, but everything is encapsulated here
return express.static("path");
}
}
export default new StaticMiddleware().run;
Finally the app.ts express app itself, which is very clean:
import staticMiddleware from "./StaticMiddleware";
import fooMiddleware from "./FooMiddleware";
import barMiddleware from "./BarMiddleware";
app.use(staticMiddleware());
app.use(fooMiddleware());
app.use(barMiddleware());
But I get an error at runtime:
TypeError: app.use() requires a middleware function
Note it's possible to change the method signatures above, so I can use this form:
app.use(staticMiddleware);
But that is surprising to a maintainer, and so liable to break. I want the normal signature:
app.use(staticMiddleware());