Added code comments (#772)

source/code-snippets/crud/startrek.js

@@ -1,12 +1,14 @@
+/* Text search */
+
 const { MongoClient } = require("mongodb");
 
-// Replace the following string with your MongoDB deployment's connection string.
-const uri =
-  "mongodb+srv://<user>:<password>@<cluster-url>?writeConcern=majority";
+// Replace the following string with your MongoDB deployment's connection string
+const uri = "mongodb+srv://<user>:<password>@<cluster-url>?writeConcern=majority";
 const client = new MongoClient(uri);
 
 async function word(movies) {
   // start word text example
+  // Create a query that searches for the string "trek"
   const query = { $text: { $search: "trek" } };
 
   // Return only the `title` of each matched document
@@ -15,21 +17,23 @@ async function word(movies) {
     title: 1,
   };
 
-  // find documents based on our query and projection
+  // Find documents based on our query and projection
   const cursor = movies.find(query).project(projection);
   // end word text example
 
-  // print a message if no documents were found
+  // Print a message if no documents were found
   if ((await movies.countDocuments(query)) === 0) {
     console.log("No documents found!");
   }
+  // Print all documents that were found
   for await (const doc of cursor) {
     console.dir(doc);
   } 
 }
 
 async function phrase(movies) {
   // start phrase text example
+  // Create a query that searches for the phrase "star trek"
   const query = { $text: { $search: "\"star trek\"" } };
 
   // Return only the `title` of each matched document
@@ -38,21 +42,23 @@ async function phrase(movies) {
     title: 1,
   };
 
-  // find documents based on our query and projection
+  // Find documents based on the query and projection
   const cursor = movies.find(query).project(projection);
   // end phrase text example
 
-  // print a message if no documents were found
+  // Print a message if no documents were found
   if ((await movies.countDocuments(query)) === 0) {
     console.log("No documents found!");
   }
+  // Print all documents that were found
   for await (const doc of cursor) {
     console.dir(doc);
   } 
 }
 
 async function negation(movies) {
   // start negation text example
+  // Create a query that searches for the phrase "star trek" while omitting "into darkness"
   const query = { $text: { $search: "\"star trek\"  -\"into darkness\"" } };
 
   // Include only the `title` field of each matched document
@@ -61,43 +67,47 @@ async function negation(movies) {
     title: 1,
   };
 
-  // find documents based on our query and projection
+  // Find documents based on the query and projection
   const cursor = movies.find(query).project(projection);
   // end negation text example
 
-  // print a message if no documents were found
+  // Print a message if no documents were found
   if ((await movies.countDocuments(query)) === 0) {
     console.log("No documents found!");
   }
+  // Print all documents that were found
   for await (const doc of cursor) {
     console.dir(doc);
   } 
 }
 
 async function relevance(movies) {
   // start relevance text example
+  // Create a query that searches for the phrase "star trek" while omitting "into darkness"r
   const query = { $text: { $search: "\"star trek\"  -\"into darkness\"" } };
 
-  // sort returned documents by descending text relevance score
+  // Sort returned documents by descending text relevance score
   const sort = { score: { $meta: "textScore" } };
+
   // Include only the `title` and `score` fields in each returned document
   const projection = {
     _id: 0,
     title: 1,
     score: { $meta: "textScore" },
   };
 
-  // find documents based on our query, sort, and projection
+  // Find documents based on the query, sort, and projection
   const cursor = movies
     .find(query)
     .sort(sort)
     .project(projection);
   // end relevance text example
 
-  // print a message if no documents were found
+  // Print a message if no documents were found
   if ((await movies.countDocuments(query)) === 0) {
     console.log("No documents found!");
   }
+  // Print all documents that were found
   for await (const doc of cursor) {
     console.dir(doc);
   } 
@@ -113,6 +123,7 @@ async function run() {
     await negation(movies);
     await relevance(movies);
   } finally {
+    // Close the database connection on completion or error
     await client.close();
   }
 }

source/code-snippets/monitoring/apm-subscribe.js

@@ -1,25 +1,27 @@
+/* Subscribe to an event */
+
 const { MongoClient } = require("mongodb");
 
-// Replace the following with your MongoDB deployment's connection
-// string.
-const uri =
-  "mongodb+srv://<clusterUrl>/?replicaSet=rs&writeConcern=majority";
+// Replace the following with your MongoDB deployment's connection string
+const uri = "mongodb+srv://<clusterUrl>/?replicaSet=rs&writeConcern=majority";
 
 const client = new MongoClient(uri, { monitorCommands:true });
 
-// Replace <event name> with the name of the event you are subscribing to.
+// Replace <event name> with the name of the event you are subscribing to
 const eventName = "<event name>";
+
+// Subscribe to a specified event and print a message when the event is received
 client.on(eventName, event => {
   console.log(`received ${eventName}: ${JSON.stringify(event, null, 2)}`);
 });
 
 async function run() {
   try {
-    // Establish and verify connection
+    // Establish and verify connection to the "admin" database
     await client.db("admin").command({ ping: 1 });
     console.log("Connected successfully");
   } finally {
-    // Ensures that the client will close when you finish/error
+    // Close the database connection on completion or error
     await client.close();
   }
 }

source/code-snippets/monitoring/cpm-subscribe.js

@@ -1,13 +1,12 @@
 const { MongoClient } = require("mongodb");
 
-// Replace the following with your MongoDB deployment's connection
-// string.
+// Replace the following with your MongoDB deployment's connection string
 const uri =
   "mongodb+srv://<clusterUrl>/?replicaSet=rs&writeConcern=majority";
 
 const client = new MongoClient(uri);
 
-// Replace <event name> with the name of the event you are subscribing to.
+// Replace <event name> with the name of the event you are subscribing to
 const eventName = "<event name>";
 
 // Subscribe to the event

source/code-snippets/monitoring/sdam-subscribe.js

@@ -1,25 +1,27 @@
+/* Subscribe to SDAM event */
+
 const { MongoClient } = require("mongodb");
 
-// Replace the following with your MongoDB deployment's connection
-// string.
-const uri =
-  "mongodb+srv://<clusterUrl>/?replicaSet=rs&writeConcern=majority";
+// Replace the following with your MongoDB deployment's connection string
+const uri = "mongodb+srv://<clusterUrl>/?replicaSet=rs&writeConcern=majority";
 
 const client = new MongoClient(uri);
 
-// Replace <event name> with the name of the event you are subscribing to.
+// Replace <event name> with the name of the event you are subscribing to
 const eventName = "<event name>";
+
+// Subscribe to a specified event and print a message when the event is received
 client.on(eventName, event => {
   console.log(`received ${eventName}: ${JSON.stringify(event, null, 2)}`);
 });
 
 async function run() {
   try {
-    // Establish and verify connection
+    // Establish and verify connection to the database
     await client.db("admin").command({ ping: 1 });
     console.log("Connected successfully");
   } finally {
-    // Ensures that the client will close when you finish/error
+    // Close the database connection on completion or error
     await client.close();
   }
 }

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

@@ -1,6 +1,8 @@
+/* Change stream listener */
+
 import { MongoClient } from "mongodb";
 
-// Replace the uri string with your MongoDB deployment's connection string.
+// Replace the uri string with your MongoDB deployment's connection string
 const uri = "<connection string uri>";
 
 const client = new MongoClient(uri);
@@ -16,28 +18,32 @@ async function run() {
     const database = client.db("insertDB");
     const haikus = database.collection("haikus");
 
-    // open a Change Stream on the "haikus" collection
+    // Open a Change Stream on the "haikus" collection
     changeStream = haikus.watch();
 
-    // set up a listener when change events are emitted
+    // Set up a change stream listener when change events are emitted
     changeStream.on("change", next => {
-      // process any change event
+      // Print any change event
       console.log("received a change to the collection: \t", next);
     });
 
+    // Pause before inserting a document
     await simulateAsyncPause();
 
+    // Insert a new document into the collection
     await myColl.insertOne({
       title: "Record of a Shriveled Datum",
       content: "No bytes, no problem. Just insert a document, in MongoDB",
     });
 
+    // Pause before closing the change stream
     await simulateAsyncPause();
 
-    await changeStream.close();
-
+    // Close the change stream and print a message to the console when it is closed
+    await changeStream.close();    
     console.log("closed the change stream");
   } finally {
+    // Close the database connection on completion or error
     await client.close();
   }
 }

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

@@ -1,19 +1,24 @@
+/* Run a database command */
+
 import { MongoClient } from "mongodb";
 
-// Replace the uri string with your MongoDB deployment's connection string.
+// Replace the uri string with your MongoDB deployment's connection string
 const uri = "<connection string uri>";
 
 const client = new MongoClient(uri);
 
 async function run() {
   try {
+    // Get the "sample_mflix" database
     const db = client.db("sample_mflix");
-    // find the storage statistics for the "sample_mflix" database using the 'dbStats' command
+
+    // Find and print the storage statistics for the "sample_mflix" database using the 'dbStats' command
     const result = await db.command({
       dbStats: 1,
     });
     console.log(result);
   } finally {
+    // Close the database connection on completion or error
     await client.close();
   }
 }

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

@@ -1,29 +1,34 @@
+/* Update multiple documents */
+
 import { MongoClient } from "mongodb";
 
-// Replace the uri string with your MongoDB deployment's connection string.
+// Replace the uri string with your MongoDB deployment's connection string
 const uri = "<connection string uri>";
 
 const client = new MongoClient(uri);
 
 async function run() {
   try {
+    // Get the "movies" collection in the "sample_mflix" database
     const database = client.db("sample_mflix");
     const movies = database.collection("movies");
 
-    // create a filter to update all movies with a 'G' rating
+    // Create a filter to update all movies with a 'G' rating
     const filter = { rated: "G" };
 
-    // increment every document matching the filter with 2 more comments
+    // Create an update document specifying the change to make
     const updateDoc = {
       $set: {
         random_review: `After viewing I am ${
           100 * Math.random()
         }% more satisfied with life.`,
       },
     };
+    // Update the documents that match the specified filter
     const result = await movies.updateMany(filter, updateDoc);
     console.log(`Updated ${result.modifiedCount} documents`);
   } finally {
+    // Close the database connection on completion or error
     await client.close();
   }
 }

source/code-snippets/usage-examples/updateMany.ts

@@ -1,3 +1,5 @@
+/* Update multiple documents */
+
 import { MongoClient } from "mongodb";
 
 // Replace the uri string with your MongoDB deployment's connection string.
@@ -13,15 +15,19 @@ enum Rating {
   NR = "NOT RATED",
 }
 
+// Create a Movie interface
 interface Movie {
   rated: Rating;
   random_review?: string;
 }
 
 async function run() {
   try {
+    // Get the "movies" collection in the "sample_mflix" database
     const database = client.db("sample_mflix");
     const movies = database.collection<Movie>("movies");
+
+    // Update all documents that match the specified filter
     const result = await movies.updateMany(
       { rated: Rating.G },
       {
@@ -34,6 +40,7 @@ async function run() {
     );
     console.log(`Updated ${result.modifiedCount} documents`);
   } finally {
+    // Close the database connection on completion or error
     await client.close();
   }
 }