quick testing for a stack of async middlewares

express-middleware-testing.js

function addField(req, res, next) {
  res.field = 1;
  next();
}

function incrementField(req, res, next) {
  res.field++;
  next();
}

function copyField(req, res, next) {
  res.fieldCopy = res.field;
  next();
}

function callMiddleware(req, res, middleware) {
  return new Promise((resolve, reject) => {
    middleware(req, res, err => {
      if (err) {
        return reject(err);
      }
      resolve();
    });
  });
}

async function callMiddlewares(req, res, middlewares) {
  for (const middleware of middlewares) {
    await callMiddleware(req, res, middleware);
  }
}

const res1 = {};
callMiddlewares({}, res1, [addField, incrementField, copyField]).then(() => {
  console.log(res1);
});

const res2 = {};
callMiddleware({}, res2, addField).then(() => {
  console.log(res2);
});