Properly set default thresholds on log appenders.

Sometimes it is useful to capture log messages in a way that is easy for
the running program to introspect or manually handle.
*BufferLogAppender* captures the logs in a simple array.

Be careful, there is no default flush/clear mechanism that runs
automatically. Users of BufferLogAppender should take care to
render/handle log messages and periodically call `clearBuffer` on the
*BufferLogAppender* instance to avoid the buffer array growing without
limit.

src/api-log-appender.ts

@@ -5,7 +5,7 @@ export class ApiLogAppender implements LogAppender {
   public batchSize = 10
   public minimumTimePassedInSec = 60
   public maximumTimePassedInSec = 120
-  public threshold = LogLevel.ALL
+  public threshold: LogLevel
 
   private msgBuffer: FlattenedLogMessage[] = []
   private lastSent = 0
@@ -16,9 +16,7 @@ export class ApiLogAppender implements LogAppender {
     threshold?: LogLevel
   ) {
     setTimeout(this.checkPost, 1000)
-    if (threshold) {
+    this.threshold = threshold ?? LogLevel.ALL
-      this.threshold = threshold
-    }
   }
 
   public appendMessage(msg: LogMessage): void {

src/buffer-log-appender.ts

@@ -0,0 +1,21 @@
+import type { LogAppender } from './log-appender'
+import { LogLevel, type LogMessage } from './log-message'
+
+export class BufferLogAppender implements LogAppender {
+  public threshold: LogLevel
+  public buffer: LogMessage[]
+
+  constructor(buffer?: LogMessage[], threshold?: LogLevel) {
+    this.buffer = buffer ?? []
+    this.threshold = threshold ?? LogLevel.ALL
+  }
+
+  public appendMessage(msg: LogMessage): void {
+    if (this.threshold && msg.level < this.threshold) return
+    else this.buffer.push(msg)
+  }
+
+  public clearBuffer(): void {
+    this.buffer.length = 0
+  }
+}

src/console-log-appender.ts

@@ -18,16 +18,12 @@ import { LogAppender } from './log-appender'
  * data for inspection in the browser's developer tools.
  */
 export class ConsoleLogAppender implements LogAppender {
-  public threshold = LogLevel.ALL
+  public threshold: LogLevel
-  public formatter: LogMessageFormatter = flattenMessage
+  public formatter: LogMessageFormatter
 
   constructor(threshold?: LogLevel, formatter?: LogMessageFormatter) {
-    if (threshold) {
+    this.threshold = threshold ?? LogLevel.ALL
-      this.threshold = threshold
+    this.formatter = formatter ?? flattenMessage
-    }
-    if (formatter) {
-      this.formatter = formatter
-    }
   }
 
   public appendMessage(msg: LogMessage): void {