Can not export function

Question

I try use function:

exports.get = async function (req, res, next) {
  filter.validateId(req,res,next);
  const db = req.app.get('db');
  let id = req.params.id;
  let user;
  try {
    user = await db.models.user.findByPk(id);
  } catch (err) {
    res.send(400)
  }
  res.json(user);
};

and exported function:

var validateId = function (req, res, next) {
  let id = parseInt(req.params.id);
  if (isNaN(id) || id <= 0) {
      res.send(400);
  }
  res.locals.id = id;

  return next();
};
exports.validateId=validateId;

But I got error:

GET /users/203 404 17.862 ms - 90

(node:20775) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client at ServerResponse.setHeader (_http_outgoing.js:470:11) at ServerResponse.header (/home/qt/dev/BigDealExpressJSTest/node_modules/express/lib/response.js:767:10) at ServerResponse.send (/home/qt/dev/BigDealExpressJSTest/node_modules/express/lib/response.js:170:12) at ServerResponse.json (/home/qt/dev/BigDealExpressJSTest/node_modules/express/lib/response.js:267:15) at exports.get (/home/qt/dev/BigDealExpressJSTest/controllers/userController.js:28:7) (node:20775) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1) (node:20775) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Answer 1

THis is wrong for couple of reasons:

First:

if (isNaN(id) || id <= 0) {
      res.send(400); //return res.send(400);
}

need to add return so that even after sending the response next() is not called.

Now for the real reason:

In validateId you are passing get function's next. So whenever you call next from validateId you are actually calling next of get thus sending the control to next middleware.

So you need to remove the filter.validateId(req,res,next); line from get function and add it as a second middlware.

ie.

exports.get = async function (req, res, next) {
  const db = req.app.get('db');
  let id = req.params.id;
  let user;
  try {
    user = await db.models.user.findByPk(id);
  } catch (err) {
    res.send(400)
  }
  res.json(user);
};

app.get('/route', validateId, get , (req,res)=>{.. do something })
or
app.get('/route', validateId, get)