ConsoleLogAppender writes a human-readable summary when logging structured data.

Taking advantage of the new LogMessageFormatter return type, the
ConsoleLogAppender logs the formatted message as-is if it is a string,
but when processing structured data inserts a string summary consisting
of the message level, scope, and message summary or method. The full
object is still logged to the console as well for inspection.

src/console-log-appender.ts

@@ -3,12 +3,23 @@ import {
   LogLevel,
   LogMessage,
   LogMessageFormatter,
-} from './log-message';
+} from "./log-message";
-import { LogAppender } from './log-appender';
+import { LogAppender } from "./log-appender";
 
+/**
+ * A log appender that writes log messages to the console. The behavior of the
+ * log appender can be configured with a threshold level and a message
+ * formatter.
+ *
+ * When the message formatter returns a string value, that value is logged to
+ * the console as-is. When the message formatter returns an object, a summary
+ * string is logged to the console, followed by the object itself. This allows
+ * logs to be easily read in the console, while still providing the structured
+ * data for inspection in the browser's developer tools.
+ */
 export class ConsoleLogAppender implements LogAppender {
   public threshold = LogLevel.ALL;
-  public formatter: LogMessageFormatter = flattenMessage
+  public formatter: LogMessageFormatter = flattenMessage;
 
   constructor(threshold?: LogLevel, formatter?: LogMessageFormatter) {
     if (threshold) {
@@ -27,17 +38,13 @@ export class ConsoleLogAppender implements LogAppender {
     let logMethod = console.log;
     switch (msg.level) {
       case LogLevel.ALL:
-        logMethod = console.log;
-        break;
       case LogLevel.TRACE:
+      case LogLevel.LOG:
         logMethod = console.log;
         break;
       case LogLevel.DEBUG:
         logMethod = console.debug;
         break;
-      case LogLevel.LOG:
-        logMethod = console.log;
-        break;
       case LogLevel.INFO:
         logMethod = console.info;
         break;
@@ -50,12 +57,25 @@ export class ConsoleLogAppender implements LogAppender {
         break;
     }
 
-    const strMsg = this.formatter(msg);
+    const fmtMsg = this.formatter(msg);
+
+    if (typeof fmtMsg === "string") {
+      if (msg.error || msg.stacktrace) {
+        logMethod(fmtMsg, msg.error ?? msg.stacktrace);
+      } else {
+        logMethod(fmtMsg);
+      }
+    } else {
+      const { message, _error, _stacktrace, ...rest } = fmtMsg;
+      const summary = `${LogLevel[msg.level]} -- ${msg.scope}: ${
+        message ?? fmtMsg.method
+      }\n`;
 
       if (msg.error || msg.stacktrace) {
-      logMethod(strMsg, msg.error ?? msg.stacktrace);
+        logMethod(summary, msg.error ?? msg.stacktrace, rest);
       } else {
-      logMethod(strMsg);
+        logMethod(summary, rest);
+      }
     }
   }
 }