How to use

each

function

in

CollectionChain

_.chain(_ids)
   .map(_id => _.find(db, a => a._id === _id))
   .compact()
   .each(a => a.retired = true)
   .value()

_.chain(_ids)
   .map(_id => _.find(db, a => a._id === _id))
   .tap(ids => console.log(ids))
   .compact()
   .each(a => a.retired = false)
   .value()

app.post('/api/surveys/webhooks', (req, res) => {
    const p = new Path('/api/surveys/:surveyId/:choice');

    _.chain(req.body)
      .map(({url, email}) => {
        const match = p.test(new URL(url).pathname);
        if (match) {
          return {email, ...match};
        }
      })
      .compact()
      .uniqBy('email', 'surveyId')
      .each(({surveyId, email, choice}) => {
        Survey.updateOne({
          _id: surveyId,
          recipients: {
            $elemMatch: {email, responded: false},
          }
        }, {
          $inc: {[choice]: 1},
          $set: {'recipients.$.responded': true},
          lastResponded: new Date(),
        }).exec();
      })
      .value();
    res.send({});
  });

.compact()
.uniqBy( 'email', 'surveyId')
.each(({ surveyId, email, choice }) => {
  Survey.updateOne({
    _id:surveyId,