Why assignment to property of function parameter is bad style.

Node.js web service

(req, res, next) => {
  req.user = Guest;
  return next();
};

Often used, can not be avoided. How should I do?

[ljharb]

The next release of eslint-config-airbnb-base, and likely eslint-config-airbnb, will include this loosening of no-param-reassign.

[shanev]

Another example is ctx in Koa routing:

router.get('/', (ctx) => {
  ctx.status = 200;
});