ob-mongo-event-preimage.js

   case 'areas': {
      if (dbOp === 'update') {
        const prevId = fullDocument?._change?.prevChangeId
        if (prevId != null) {
          const area = await getChangeLogModel().aggregate([
            { $match: { _id: prevId } },
            {
              $project:
              {
                changes: {
                  $filter: {
                    input: '$changes',
                    as: 'item',
                    cond: { $eq: ['$$item.fullDocument._id', fullDocument._id] }
                  }
                }
              }
            },
            {
              $unwind: '$changes'
            }])
          console.log('# get previous', area[0].changes.fullDocument)
          console.log('# get current', fullDocument)

          const diff = Diff.diffJson(area[0].changes.fullDocument.children, fullDocument.children, { ignoreWhitespace: true })
          console.log('#diff', diff)
        }
      }