DOCSP-18158 updated change stream example (#256)

* updated change stream example

Author: kyuan-mongodb

source/code-snippets/usage-examples/changeStream.js

@@ -5,39 +5,41 @@ const uri = "<connection string uri>";
 
 const client = new MongoClient(uri);
 
+const simulateAsyncPause = () =>
+  new Promise(resolve => {
+    setTimeout(() => resolve(), 1000);
+  });
+
 let changeStream;
 async function run() {
   try {
     await client.connect();
-    const database = client.db("sample_mflix");
-    const movies = database.collection("movies");
+    const database = client.db("insertDB");
+    const collection = database.collection("haikus");
 
-    // open a Change Stream on the "movies" collection
-    changeStream = movies.watch();
+    // open a Change Stream on the "haikus" collection
+    changeStream = collection.watch();
 
     // set up a listener when change events are emitted
     changeStream.on("change", next => {
       // process any change event
       console.log("received a change to the collection: \t", next);
     });
 
-    // use a timeout to ensure the listener is registered before the insertOne
-    // operation is called.
-    await new Promise(resolve => {
-      setTimeout(async () => {
-        await movies.insertOne({
-          test: "sample movie document",
-        });
-        // wait to close `changeStream` after the listener receives the event
-        setTimeout(async () => {
-          resolve(
-            await changeStream.close(() => console.log("closed the change stream"))
-          );
-        }, 1000);
-      }, 1000);
+    await simulateAsyncPause();
+
+    await collection.insertOne({
+      title: "Record of a Shriveled Datum",
+      content: "No bytes, no problem. Just insert a document, in MongoDB",
     });
+
+    await simulateAsyncPause();
+
+    await changeStream.close();
+    
+    console.log("closed the change stream");
   } finally {
     await client.close();
   }
 }
-run().catch(console.dir);
+run().catch(console.dir);

source/usage-examples/changeStream.txt

@@ -14,7 +14,7 @@ change stream emits **change event** documents when they occur.
 The ``watch()`` method optionally takes an **aggregation pipeline** which consists of an array of **aggregation stages**
 as the first parameter. The aggregation stages filter and transform the change events.
 
-In the example below, the ``$match`` stage will match all change event documents with a ``runtime`` value of less than
+In the following snippet, the ``$match`` stage matches all change event documents with a ``runtime`` value of less than
 15, filtering all others out.
 
 .. code-block:: javascript
@@ -82,23 +82,23 @@ methods presented above:
 Example
 -------
 
-The following example opens a change stream on the ``movies`` collection in
-the ``sample_mflix`` database. Let's create a listener function to receive and
+The following example opens a change stream on the ``haikus`` collection in
+the ``insertDB`` database. Let's create a listener function to receive and
 print change events that occur on the collection.
 
 First, open the change stream on the collection and then define a callback
 on the change stream using the ``on()`` method. Once set, generate a change
-event to be emitted by performing a change to the collection.
+event by performing a change to the collection.
 
 To generate the change event on the collection, let's use ``insertOne()``
 method to add a new document. Since the ``insertOne()`` may run before the
-listener function can register, we use a timer, declared with ``setTimeout()``
-to wait one second before executing the insert.
+listener function can register, we use a timer, defined as
+``simulateAsyncPause`` to wait 1 second before executing the insert.
 
-We also use a second timer to wait an additional second after the insertion of
-the document to provide ample time for the change event to be received and
-the for the callback to complete its execution before closing the
-``ChangeStream`` instance using the ``close()`` method.
+We also use ``simulateAsyncPause`` after the insertion of the document
+to provide ample time for the listener function to receive the change
+event and for the callback to complete its execution before 
+closing the ``ChangeStream`` instance using the ``close()`` method.
 
 The timers used in this example are only necessary for this demonstration
 to make sure there is enough time to register listener and have the
@@ -133,14 +133,12 @@ If you run the preceding example, you should see the following output:
    :copyable: false
 
    received a change to the collection: 	 {
-     _id: {
-       _data: '825EC...'
-     },
+     _id: { _data: '825EC...' },
      operationType: 'insert',
-     clusterTime: Timestamp { ... },
-     fullDocument: { _id: 5ec3..., test: 'sample movie document' },
-     ns: { db: 'sample_mflix', coll: 'movies' },
-     documentKey: { _id: 5ec3... },
+     clusterTime: new Timestamp { ... },
+     fullDocument: { _id: new ObjectId(...), title: 'Record of a Shriveled Datum', content: 'No bytes, no problem. Just insert a document, in MongoDB' },
+     ns: { db: 'insertDB', coll: 'haikus' },
+     documentKey: { _id: new ObjectId(...) }
    }
    closed the change stream