optimize logger child and consumer performance

Author: mertcanaltin

lib/logger.js

@@ -60,7 +60,6 @@ function noop() {}
  * Consumers subscribe to diagnostics_channel events
  */
 class LogConsumer {
-  #level;
   #levelValue;
 
   constructor(options = kEmptyObject) {
@@ -168,11 +167,25 @@ class JSONConsumer extends LogConsumer {
       level: record.level,
       time: record.time,
       msg: record.msg,
-      ...this.#fields,
-      ...record.bindings,
-      ...record.fields,
     };
 
+    // Merge fields in order: consumer fields -> bindings -> log fields
+    // Using direct property assignment for better performance
+    const consumerFields = this.#fields;
+    for (const key in consumerFields) {
+      logObj[key] = consumerFields[key];
+    }
+
+    const bindings = record.bindings;
+    for (const key in bindings) {
+      logObj[key] = bindings[key];
+    }
+
+    const fields = record.fields;
+    for (const key in fields) {
+      logObj[key] = fields[key];
+    }
+
     const json = JSONStringify(logObj) + '\n';
     this.#stream.write(json);
   }
@@ -270,10 +283,12 @@ class Logger {
       bindings,
     );
 
-    return new Logger({
+    const childLogger = new Logger({
       level: options.level || this.#level,
       bindings: mergedBindings,
     });
+
+    return childLogger;
   }
 
   /**