subclass.js

class Router {
  static build(stuff) {
    // Compute compute
    // var constructorArg = 123
    return new Router(constructorArg)
  }

  new Router(constructorArg)

  route(location) {
    return promise
  }
}

class MyRouter {
  route(location) {
    console.log('begin routing ' + location)
    return super(location)
      .finally(function() {
        console.log('end routing ' + location)
      })
  }

  // Yes, I want to inherit .build here, so MyRouter.build(stuff) works.
  //
  // And if `build` was a `call constructor` instead, I'd want to inherit that.
}