错误地调用了firestore快照之间的视图更改

Question

i am doing a toast that notifies admin about events happening in firestore but when i reload the web page the added event is called with the same number of documents?

 db.collection("Bill").where('UserSell', '==', ad.getAdmin).onSnapshot(
            (doc) => {
                doc.docChanges().forEach(function (a) {
                   
                    if (a.type === "added") {
                        toastr.options.progressBar = true;
                        toastr.options.showMethod = 'slideDown';
                        toastr.success('a new invoice has just been added', 'Mess')
                     }
                   }
)

but when I reload the page it shows the number of toast = number of documents even though I didn't call the click add event

Answer 1

The event types are relative to the listener you attach. So when you just attach the listener, the first time its callback is called all documents are newly added to that listener. This is the expected behavior.

If you want to know whether a document is "new" by some other measure, you should include information for that purpose in the document itself. For example, it is quite common to include timestamp fields in each document of when it was created and when it was last updated. You can then keep a timestamp in each client of when it last loaded data, and use that to create a query for documents that were created or updated since then.