docs: update docs about logging additional keys

Author: Dmitry Balabanov

docs/core/logger.md

@@ -276,10 +276,12 @@ You can append additional persistent keys and values in the logs generated durin
 ### Appending additional log keys and values to a single log item
 
 You can append additional keys and values in a single log item passing them as parameters.
+Pass a string for logging it with default key name `extra`. Alternatively, pass one or multiple objects with custom keys.
+If you already have an object containing a `message` key and an additional property, you can pass this object directly.
 
 === "handler.ts"
 
-    ```typescript hl_lines="14 18-19"
+    ```typescript hl_lines="14 18-19 23 31"
     import { Logger } from '@aws-lambda-powertools/logger';
 
     const logger = new Logger();
@@ -300,6 +302,17 @@ You can append additional keys and values in a single log item passing them as p
             { data: myImportantVariable },
             { correlationIds: { myCustomCorrelationId: 'foo-bar-baz' } }
         );
+
+        // Simply pass a string for logging additional data
+        logger.info('This is a log with additional string value', 'string value');
+
+        // Directly passing an object containing both the message and the additional info
+        const logObject = {
+            message: 'This is a log message',
+            additionalValue: 42
+        };
+
+        logger.info(logObject);
         
         return {
             foo: 'bar'
@@ -309,7 +322,7 @@ You can append additional keys and values in a single log item passing them as p
     ```
 === "Example CloudWatch Logs excerpt"
 
-    ```json hl_lines="7 15-16"
+    ```json hl_lines="7 15-16 24 32"
     {
         "level": "INFO",
         "message": "This is a log with an extra variable",
@@ -327,6 +340,22 @@ You can append additional keys and values in a single log item passing them as p
         "data": { "foo": "bar" },
         "correlationIds": { "myCustomCorrelationId": "foo-bar-baz" }
     }
+    {
+        "level": "INFO",
+        "message": "This is a log with additional string value",
+        "service": "serverlessAirline",
+        "timestamp": "2021-12-12T22:06:17.463Z",
+        "xray_trace_id": "abcdef123456abcdef123456abcdef123456",
+        "extra": "string value"
+    }
+    {
+        "level": "INFO",
+        "message": "This is a log message",
+        "service": "serverlessAirline",
+        "timestamp": "2021-12-12T22:06:17.463Z",
+        "xray_trace_id": "abcdef123456abcdef123456abcdef123456",
+        "additionalValue": 42
+    }
     ```
 
 ### Logging errors
@@ -347,14 +376,14 @@ The error will be logged with default key name `error`, but you can also pass yo
             throw new Error('Unexpected error #1');
         } catch (error) {
             // Log information about the error using the default "error" key
-            logger.error('This is the first error', error);
+            logger.error('This is the first error', error as Error);
         }
 
         try {
             throw new Error('Unexpected error #2');
         } catch (error) {
             // Log information about the error using a custom "myCustomErrorKey" key
-            logger.error('This is the second error', { myCustomErrorKey: error } );
+            logger.error('This is the second error', { myCustomErrorKey: error as Error } );
         }
 
     };
@@ -391,6 +420,9 @@ The error will be logged with default key name `error`, but you can also pass yo
     }
     ```
 
+!!! tip "Logging errors and log level"
+    You can also log errors using the `warn`, `info`, and `debug` methods. Be aware of the log level though, you might miss those  errors when analyzing the log later depending on the log level configuration.
+
 ## Advanced
 
 ### Using multiple Logger instances across your code