This is awesome change, would help debug various issues when deserialization fails when class or other element is not registered or it's module not imported. Would love to have that merged! ❤️

wonderful change, thank you! could you add a test for it?

@Skn0tt tried for a while now and I can't seem to make it throw that error in tests, can I get some help with this? :)

Try this:

❯ git diff src
diff --git a/src/index.test.ts b/src/index.test.ts
index e314728..ee49e72 100644
--- a/src/index.test.ts
+++ b/src/index.test.ts
@@ -810,6 +810,9 @@ describe('stringify & parse', () => {
       );
       expect(deserialized.s7).toBeInstanceOf(Train);
       expect(typeof deserialized.s7.brag()).toBe('string');
+
+      meta.values.s7 = [['class', 'Plane']];
+      expect(() => SuperJSON.deserialize(JSON.parse(JSON.stringify({ json, meta })))).toThrowError(`Trying to deserialize unknown class 'Plane' - check https://github.com/blitz-js/superjson/issues/116#issuecomment-773996564`)
     });
 
     describe('with accessor attributes', () => {

Try this:

❯ git diff src
diff --git a/src/index.test.ts b/src/index.test.ts
index e314728..ee49e72 100644
--- a/src/index.test.ts
+++ b/src/index.test.ts
@@ -810,6 +810,9 @@ describe('stringify & parse', () => {
       );
       expect(deserialized.s7).toBeInstanceOf(Train);
       expect(typeof deserialized.s7.brag()).toBe('string');
+
+      meta.values.s7 = [['class', 'Plane']];
+      expect(() => SuperJSON.deserialize(JSON.parse(JSON.stringify({ json, meta })))).toThrowError(`Trying to deserialize unknown class 'Plane' - check https://github.com/blitz-js/superjson/issues/116#issuecomment-773996564`)
     });
 
     describe('with accessor attributes', () => {

Thank you, got it working.