How to use setOnInsert to place created/updated field in mongodb?

Question

I'm using a nodejs client to loop over input and create an array of values that will be handed off to the bulkWrite operation:

  var updateVal = { sku: item.sku, name: item.name, updatedAt: new Date()};
  var insertVal = { sku: item.sku, name: item.name, createdAt: new Date(), updatedAt: new Date()};
  itemsToSave.push({
    updateOne: {
      filter: {
        sku: item.sku
      },
      //update: { $set: updateVal }, // works
      //update: { $setOnInsert: insertVal }, // works
      update: { $set: updateVal, $setOnInsert: insertVal }, // DOES NOT work
      upsert:true
    }
  });

But for some reason I can't mix $set and $setOnInsert ... when I run it, nothing happens, it is like a no-op. Is this a limitation of bulk operation?

I'm using node-mongodb-native/2.1 to work with mongodb 3.0.7

The docs for setOnInsert suggest that this should be possible:

...
  {
     $set: { item: "apple" },
     $setOnInsert: { defaultQty: 100 }
  },
  { upsert: true }

That's why my question is about using it with bulkWrite

Update

This worked:

      update: {
        $currentDate: { updatedAt: true },
        $set: updateVal,
        $setOnInsert: {
          createdAt: new Date()
        }
      },
      upsert:true

thanks to the sample found via github code search: https://github.com/rainder/node-process-stat/blob/22899f49413314402645ae57bc691bd389d226bd/src/server/router/log.js#L49-L59

Helsell