code: function emit (route, req, res) {
      assert.equal(typeof route, 'string')
      assert.ok(req, 'no req specified')
  
      if (!req._ssa) {
        assert.ok(res, 'no res specified')
      }
  
      // handle server init
      if (isReq(req) && isRes(res)) {
        const ssa = createSsa({}, req, res)
        const dft = { node: { cb: [ router._default ] } }
        return router(route, ssa, dft)
      }
  
      // handle subrouter
      const params = req
      const parentDefault = res
      router(route, params, parentDefault)
    }
docs: match a route and execute the corresponding callback (obj, obj) -> null original: {path, params parentDefault}