Name property of anonymous class extending another classes is set inconsistently

[StenCalDabran]

Setup

• Version: one behaviour for latest 12 (12.19.0) and 15 versions (15.0.1), the other behaviour for the latest 14 (14.15.0) and older 12 versions (e.g. 12.13.0)
• Platform: Platform-independent (same behaviour on Windows, Mac and within Docker container)
• Subsystem: ?

What steps will reproduce the bug?

Run the following Javascript code

class SomeClass {}
console.log('Anonymous name property is:', class extends SomeClass {}.name);

How often does it reproduce? Is there a required condition?

No additional conditions beside node version.

What is the expected behavior?

I am not sure what the expected behaviour is, but it should be consistent at least for all latest minor versions of still supported major versions

What do you see instead?

For version 12.19.0 and 15.0.1 the name property of the anonymous class is an empty string.
For version 12.13.0 and 14.15.0 the name property of the anonymous class is the name of the extended class, i.e. 'SomeClass' in the example.

[devsnek]

JS was changed recently to always set the name property on anonymous functions/classes. Prior to this, you were just seeing the name property from the class it extends due to prototypal inheritance.

[StenCalDabran]

Ok, so if the expected behaviour now is that the name property of the extended class always gets overwritten, then this should also happen in the latest stable version? It seems weird that this change is already implemented in the latest 12 version but not yet in the latest 14 version.

[aduh95]

The spec change happened in tc39/ecma262@74a9ef8, and it's been implemented in V8 7.8 (v8/v8@48c9ca4) which is why Node.js v12.16+ shows the correct behaviour. However it's been reverted by v8/v8@1b594a2 that landed in V8 8.0 (Node.js v14 uses V8 8.4). It's since been re-implemented by v8/v8@048761a, which landed in V8 8.6 / Node.js v15.0.0.
I've found the info in the V8:9646 bug ticket.

@StenCalDabran If you'd like to fix the behaviour of Node.js v14.x, you can open a backport PR to cherry-pick v8/v8@048761a onto v14.x-staging.

[targos]

v14.x is now in Maintenance. Only critical bug fixes can land on it.