ChangeStream not working according to this document, the next function must return null if no exist anymore document but for me not working.
this is my code :

 while (await changeStreamIterator.hasNext()) {
                let change = await;
                if (change == null)

Hello @Pejman_Azad, welcome to the MongoDB Community forum.

Within the while loop, in the statement let change = await; the variable change has a Change Event document.

The loop waits until there is a change in the collection (or database or the deployment). The change event document will have the info about the change (i.e., about the update on the collection).

For example:

There is a collection called mycoll and as I do insert, update or modify operations on it, the change stream on the collection will notify the changes:

const database = client.db("test");
const collection = database.collection("coll");
const changeStream =;

while (await changeStream.hasNext()) {
    let change = await;
    if (change == null) console.log("event doc was null!!");
    console.log(change);                              // notified change event document

When a document is inserted/updated/deleted in the mycoll the change event document is printed. For example, a delete generates this change document:

  _id: {
    _data: '825FFED...D986AE41A80004'
  operationType: 'delete',
  clusterTime: Timestamp { _bsontype: 'Timestamp', low_: 1, high_: 1610536524 },
  ns: { db: 'test', coll: 'mycoll' },
  documentKey: { _id: 5ffed280937038d986ae41a8 }

In case of a condition where the change event document cannot be generated then there will be a null - I suspect it might be some kind of error or abnormal condition (I coudn’t find any documentation on this).

Meanwhile the change stream cursor remains open until one of these occur - the cursor is explicitly closed or an invalidate event occurs - and then exists the loop.