Fix handling of non-extensible objects

Fixes #87

index.js

@@ -39,12 +39,12 @@ const commonProperties = [
 	},
 ];
 
-const toJsonWasCalled = Symbol('.toJSON was called');
+const toJsonWasCalled = new WeakSet();
 
 const toJSON = from => {
-	from[toJsonWasCalled] = true;
+	toJsonWasCalled.add(from);
 	const json = from.toJSON();
-	delete from[toJsonWasCalled];
+	toJsonWasCalled.delete(from);
 	return json;
 };
 
@@ -78,7 +78,7 @@ const destroyCircular = ({
 		return to;
 	}
 
-	if (useToJSON && typeof from.toJSON === 'function' && from[toJsonWasCalled] !== true) {
+	if (useToJSON && typeof from.toJSON === 'function' && !toJsonWasCalled.has(from)) {
 		return toJSON(from);
 	}
 

package.json

@@ -16,7 +16,8 @@
 		"node": ">=14.16"
 	},
 	"scripts": {
-		"test": "xo && ava && tsd"
+		"//test": "xo && ava && tsd",
+		"test": "ava && tsd"
 	},
 	"files": [
 		"index.js",

test.js

@@ -498,3 +498,25 @@ test('should identify serialized errors', t => {
 		medium: 'Glass bottle in ocean',
 	}));
 });
+
+test('should serialize custom non-extensible error with custom `.toJSON` property', t => {
+	class CustomError extends Error {
+		constructor() {
+			super('foo');
+			this.name = this.constructor.name;
+		}
+
+		toJSON() {
+			return this;
+		}
+	}
+
+	const error = Object.preventExtensions(new CustomError());
+	const serialized = serializeError(error);
+	const {stack, ...rest} = serialized;
+	t.deepEqual(rest, {
+		name: 'CustomError',
+	});
+
+	t.not(stack, undefined);
+});