How to call function every time collection updates from server? - meteor

Question

For example, in this controller parties object autoupdates when another user changes Paries collection, but how do we catch this update and run some controller logic?
this.helpers({ parties: () => Parties.find({}) });
SPECIFIED QUESTION:
Recieved answers do not solve my problem as it's not server logic or any database manipulations that I need to perform upon update. Actually it's controller logic that I need to run.
In the following example I disable submit button if form is not changed. isFormChange function compares party with originalParty. I need to redefine originalParty value when party changes from server side. So how can I do this?
<form ng-submit="vm.updateParty()">
<input type="text" ng-model="vm.party.name">
<input type="submit" ng-disabled="!vm.isFormChanged()" value="Submit">
</form>
directive controller:
function Ctrl($scope, $reactive) {
let vm = this;
$reactive(vm).attach($scope);
vm.helpers({ party: () => Parties.findOne({_id: vm.partyId}) });
let originalParty = angular.copy(vm.party);
vm.isFormChanged = isFormChanged;
vm.updateParty = updateParty;
function isFormChanged() {
return !angular.equals(vm.party, originalParty);
}
function updateParty() {
Meteor.call('updateParty', vm.party._id, vm.party.name);
}
}

Answer 1

Use the collection-hooks package to run code before or after updates, upserts, inserts, and removes.
myCollection.after.update(userId, doc, fieldNames, modifier, options){
...your code
}

Answer 2

You can run your logic on the server, if you have your database functionality in Meteor methods.
Example:
Parties = new Mongo.Collection("parties");
if (Meteor.isClient) {
// This code only runs on the client
Meteor.subscribe("parties");
/* a helper or event can run the Meteor.call() */
var partyData = {}; // get partyData
Meteor.call("insertParty", partyData,
// callback function
function (error, result) {
if (error) { console.log(error); };
});
}
if (Meteor.isServer) {
// This code only runs on the server
Meteor.publish("parties", function () {
return Parties.find({});
});
Meteor.methods({
insertParty: function (partyData) {
// insert logic to run on partyData here
Parties.insert(partyData);
}
})
}