mongodb stitch function for database trigger to save updated_at and created_at

source.js

exports = function(changeEvent) {
  console.log("changed", changeEvent.operationType, JSON.stringify(Object.keys(changeEvent)))
  //allows replace and create
  if(changeEvent.operationType == "update") {
    let keys = Object.keys(changeEvent.updateDescription.updatedFields)
    console.log("changed", JSON.stringify(Object.keys(changeEvent.updateDescription.updatedFields)))
    if(keys.indexOf('created_at') > -1 || keys.indexOf('updated_at') > -1 || keys.length == 0) {
      //changed fields contains created_at or updated_at
      //  on $set, it will trigger "update"
      console.log("ignoring change")
      return
    }
  }
  
  let now = new Date();
  now = new Date(now.toUTCString());
  var docId = changeEvent.documentKey._id;
  console.log("on", changeEvent.operationType, changeEvent.ns.coll, docId)
  collection = context.services.get("c0").db("d1").collection(changeEvent.ns.coll);
  
  if(changeEvent.operationType == "insert") {
    collection.updateOne({ _id : docId }, { $set: { created_at : now, updated_at : now } } )
  } else {
    collection.updateOne({ _id : docId }, { $set: { updated_at : now } } )
  }
};