feat: add onDebug overload

This support the most common usage.

README.md

@@ -35,6 +35,9 @@ log.onWarn(...)
 log.onInfo(...)
 log.onDebug(...)
 
+// or
+log.onError(() => getLogMessageThatIsTimeConsumingToCreate())
+
 function getLogMessageThatIsTimeConsumingToCreate() {
   ...
 }

src/Logger.ts

@@ -50,7 +50,10 @@ export class LoggerImpl implements ALogger {
   }
 
   private on(logLevel, logFunction) {
-    if (this.level >= logLevel)
-      logFunction(this.logger[logLevelNameMap[logLevel]].bind(this.logger))
+    if (this.level >= logLevel) {
+      const logFn = this.logger[logLevelNameMap[logLevel]].bind(this.logger)
+      const result = logFunction(logFn)
+      if (result) logFn(result)
+    }
   }
 }

src/getLogger.spec.ts

@@ -267,3 +267,18 @@ test('on???() logs to corresponding log', t => {
     'error'
   ])
 })
+
+test(`pass '() => string' into on???() will log the result`, t => {
+  const log = getLogger('onXXX with () => string')
+  log.setLevel(logLevel.debug)
+  log.onDebug(() => 'debug')
+  log.onInfo(() => 'info')
+  log.onWarn(() => 'warn')
+  log.onError(() => 'error')
+  t.deepEqual(appender.logs.map(l => l.messages[0]), [
+    'debug',
+    'info',
+    'warn',
+    'error'
+  ])
+})

src/interfaces.ts

@@ -9,8 +9,8 @@ export interface Logger extends ALogger {
   error(...args: any[]): void
   setLevel(level: number): void
 
-  onError(logFunction: (log: logMethod) => void): void
-  onWarn(logFunction: (log: logMethod) => void): void
-  onInfo(logFunction: (log: logMethod) => void): void
-  onDebug(logFunction: (log: logMethod) => void): void
+  onError(logFunction: ((log: logMethod) => void) | (() => string)): void
+  onWarn(logFunction: ((log: logMethod) => void) | (() => string)): void
+  onInfo(logFunction: ((log: logMethod) => void) | (() => string)): void
+  onDebug(logFunction: ((log: logMethod) => void) | (() => string)): void
 }