DOCSP-10362: Address feedback on Logging page (#101)

Author: Chris Cho

source/code-snippets/logging/levels.js

@@ -1,8 +1,8 @@
 // ignored first line
+// begin-ex
 const { MongoClient, Logger } = 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&w=majority";
 
@@ -17,6 +17,8 @@ async function main(client) {
   // Run a sample command to produce logger messages
   await db.command({ isMaster: true });
 }
+// end-ex
+
 
 async function run() {
   try {

source/fundamentals/logging.txt

@@ -51,20 +51,42 @@ level:
 
 .. literalinclude:: /code-snippets/logging/levels.js
    :language: javascript
+   :start-after: begin-ex
+   :end-before: end-ex
    :dedent: 4
 
+This snippet should output a few lines of logging information that
+resemble the following:
+
+.. code-block:: none
+
+   [DEBUG-Db:63846] 1585699200000 executing command {"isMaster":true} against sample_mflix.$cmd with options [{"readPreference":{"mode":"primary"}}] {
+     type: 'debug',
+     message: 'executing command {"isMaster":true} against sample_mflix.$cmd with options [{"readPreference":{"mode":"primary"}}]',
+     className: 'Db',
+     ...,
+   }
+   [DEBUG-Server:63846] 1585699200000 executing command [{"ns":"sample_mflix.$cmd","cmd":{"isMaster":true},"options":{}}] against myClusterHostname:27017:27017 {
+     ...
+   }
+   [DEBUG-Server:63846] 11585699200000 executing command
+   [{"ns":"admin.$cmd","cmd":{"endSessions":[{"id":"DQLUQ1/LRKOYMy2CD13iLQ=="}]},"options":{}}] against myClusterHostname:27017 {
+     ...
+   }
+
+
 Filter on a Specific Class
 --------------------------
 
 You can set the Logger to only produce log messages generated by specific
-classes. The following example demonstrates how to log messages from the
-``Db`` class only.
+classes by defining a filter on it. The following example demonstrates how to
+apply a filter to log messages from the ``Db`` class only.
 
 .. code-block:: js
 
-   async function main(client) {
      // Set debug level
      Logger.setLevel("debug");
+
      // Only log statements on "Db" class
      Logger.filter("class", ["Db"]);
 
@@ -74,7 +96,20 @@ classes. The following example demonstrates how to log messages from the
      await db.command({ isMaster: true });
    }
 
-You can specify the following driver classes for the logging filter:
+The logger output of the code above is similar to the prior example, but
+excludes logging from classes other than ``Db`` such as ``Server`` and
+resembles the following:
+
+.. code-block:: none
+
+   [DEBUG-Db:63846] 1585699200000 executing command {"isMaster":true} against sample_mflix.$cmd with options [{"readPreference":{"mode":"primary"}}] {
+     type: 'debug',
+     message: 'executing command {"isMaster":true} against sample_mflix.$cmd with options [{"readPreference":{"mode":"primary"}}]',
+     className: 'Db',
+     ...
+
+You can specify any number of the following driver classes in the logging
+filter array to control what information is passed to the Logger:
 
 .. list-table::
    :header-rows: 1
@@ -107,7 +142,7 @@ You can specify the following driver classes for the logging filter:
    * - ``Ping``
      - Information related to a replica set ping operation.
 
-You can add your own classes to the logger filter by creating your own logger
+You can add your own classes to the logger by creating your own logger
 instances as shown in the following sample code.
 
 .. code-block:: js
@@ -126,37 +161,63 @@ instances as shown in the following sample code.
      }
    }
 
-   // Execute A
+   // Execute A to produce logging messages
    const a = new A();
    a.doSomething();
 
+The logging message is triggered when ``doSomething()`` is called and is
+presented in the following format:
+
+.. code-block:: none
+
+   [INFO-A:65156] 1585699200000 logging A {
+     type: 'info',
+     message: 'logging A',
+     className: 'A',
+     ...
+   }
+
+
 Custom Logger
 -------------
 
 You can configure the behavior and format of the messages reported by the
-logger by passing in a
-:node-api:`logger callback function <Logger.html#~loggerCallback>` which
-allows you to access and modify the message and metadata of the logger
-message.
+logger by passing in a **logger callback function** which allows you
+to access and modify the message and metadata of the logger message.
 
-The following example demonstrates how to define a custom logger.
+The following example demonstrates how to define a logger callback
+function and add custom logic to it.
 
 .. code-block:: js
 
-   async function main(client) {
-     // Set debug level
-     Logger.setLevel("debug");
+   // Set debug level
+   Logger.setLevel("debug");
 
-     // Set our own logger
-     Logger.setCurrentLogger((msg, context) => {
-       // Add your custom logic here
-       console.log(msg, context);
-     });
+   // Set our own logger
+   Logger.setCurrentLogger((msg, context) => {
+     // Add your custom logic here
+     context['foo'] = 'bar';
+     msg = "Hello, World! " + msg;
 
-     const db = client.db("sample_mflix");
+     console.log(msg, context);
+   });
 
-     // Execute command { isMaster: true } against db to produce log messages
-     await db.command({ isMaster: true });
+   const db = client.db("sample_mflix");
+
+   // Run a command to produce logger messages
+   await db.command({ isMaster: true });
+
+The code example above adds additional information in the callback function.
+The output of the example resembles the following:
+
+.. code-block:: none
+
+   Hello, World! [DEBUG-Db:65873] 1585699200000 executing command {"isMaster":true} against sample_mflix.$cmd with options [{"readPreference":{"mode":"primary"}}] {
+     type: 'debug',
+     message: 'executing command {"isMaster":true} against sample_mflix.$cmd with options [{"readPreference":{"mode":"primary"}}]',
+     className: 'Db',
+     foo: 'bar',
+     ...
    }
 
 For more information on the methods available on the ``Logger``, see the