Fix logging for objects that define toJSON

CHANGELOG.md

@@ -1,4 +1,5 @@
 - Adds support for setting user labels on functions via `runWith()`.
 - Adds support for FIREBASE_CONFIG env as the name of a JSON file
+- Fixes an issue where objects that define `toJSON` could not be logged successfully (#907).
 - Formalize module exports. Loggers can now be accessed at 'firebase-functions/logger' and 'firebase-functions/logger/compat'
 - Fixes an issue where Remote Config coiuld not be emulated in Windows machines on the classic Command Prompt.

spec/logger.spec.ts

@@ -1,4 +1,5 @@
 import { expect } from 'chai';
+
 import * as logger from '../src/logger';
 
 const SUPPORTS_STRUCTURED_LOGS =
@@ -109,6 +110,22 @@ describe(`logger (${
           });
         });
 
+        it('should not break on objects that override toJSON', () => {
+          const obj: any = { a: new Date('August 26, 1994 12:24:00Z') };
+
+          const entry: logger.LogEntry = {
+            severity: 'ERROR',
+            message: 'testing toJSON',
+            obj,
+          };
+          logger.write(entry);
+          expectStderr({
+            severity: 'ERROR',
+            message: 'testing toJSON',
+            obj: { a: '1994-08-26T12:24:00.000Z' },
+          });
+        });
+
         it('should not alter parameters that are logged', () => {
           const circ: any = { b: 'foo' };
           circ.array = [circ];

src/logger/index.ts

@@ -35,6 +35,10 @@ function removeCircular(obj: any, refs: any[] = []): any {
   if (typeof obj !== 'object' || !obj) {
     return obj;
   }
+  // If the object defines its own toJSON, prefer that.
+  if (obj['toJSON']) {
+    return obj.toJSON();
+  }
   if (refs.includes(obj)) {
     return '[Circular]';
   } else {