nodejs util inspect custom symol

Author: enisdenjo

packages/logger/src/utils.ts

@@ -128,6 +128,8 @@ function isPrimitive(val: unknown): val is string | number | boolean {
   return val !== Object(val);
 }
 
+const nodejsCustomInspectSy = Symbol.for('nodejs.util.inspect.custom');
+
 function objectifyClass(val: unknown): Record<string, unknown> {
   if (
     // simply empty
@@ -145,6 +147,19 @@ function objectifyClass(val: unknown): Record<string, unknown> {
     // if the object has a toJSON method, use it - always
     return val.toJSON();
   }
+  if (
+    typeof val === 'object' &&
+    nodejsCustomInspectSy in val &&
+    typeof val[nodejsCustomInspectSy] === 'function'
+  ) {
+    // > Custom [util.inspect.custom](depth, opts, inspect) functions typically return a string but may return a value of any type that will be formatted accordingly by util.inspect().
+    return {
+      [nodejsCustomInspectSy.toString()]: unwrapAttrVal(
+        val[nodejsCustomInspectSy](Infinity, {}),
+      ),
+      class: val.constructor.name,
+    };
+  }
   const props: Record<string, unknown> = {};
   for (const propName of Object.getOwnPropertyNames(val)) {
     props[propName] = unwrapAttrVal(val[propName as keyof typeof val]);

packages/logger/tests/logger.test.ts

@@ -784,3 +784,28 @@ it('should change child log level only on child', () => {
     ]
   `);
 });
+
+it('should log using nodejs.util.inspect.custom symbol', () => {
+  const [log, writer] = createTLogger();
+
+  class Inspect {
+    [Symbol.for('nodejs.util.inspect.custom')]() {
+      return 'Ok good';
+    }
+  }
+
+  log.info(new Inspect(), 'sy');
+
+  expect(writer.logs).toMatchInlineSnapshot(`
+    [
+      {
+        "attrs": {
+          "Symbol(nodejs.util.inspect.custom)": "Ok good",
+          "class": "Inspect",
+        },
+        "level": "info",
+        "msg": "sy",
+      },
+    ]
+  `);
+});