14.6+ changed C++ addon behaviour of toString

[nschonni]

• Version: 14.6
• Platform: Windows, Linux, OSX, Alpine
• Subsystem: x86 and x64

What steps will reproduce the bug?

Calling .toString on an object now returns [object Object], instead of [object TheType]

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

Always

What is the expected behavior?

The type of the object should be printed like [object TheType]

What do you see instead?

Calling toString returns [object Object]

Additional information

You can see test covering this started to fail in 14.6 and above sass/node-sass@1f6b7f8, but are passing for previous node majors, and ok with 14.5 sass/node-sass@fd7ac32

Example test that fails on 14.6+

https://github.com/sass/node-sass/blob/1bab0ad3c888f9de8099d7faa750ba4fc83e9c0a/test/types.js#L17-L23

Node-sass used to be covered by CITGM, but maybe it was removed

/cc @xzyfer

[nschonni]

Ah, looks like it was disabled in CITGM in nodejs/citgm#790, before 14.6 came out

[bnoordhuis]

v8/v8@1aa51b498e2 is the change and chromium:793406 the upstream bug report (tl;dr spec conformity.)

I'll close this out: not a bug and not under our control.

edit: forgot to mention: the V8 8.3 -> 8.4 upgrade in v14.6.0 contains that change.

[nschonni]

Thanks @bnoordhuis I figured it was probably from the v8 change. Is there any hint to implementing the @@toStringTag in a why that maintains backwards compatibility with 10 and 12? It used to be picking up the value from https://github.com/sass/node-sass/blob/1bab0ad3c888f9de8099d7faa750ba4fc83e9c0a/src/sass_types/color.h#L18

[bnoordhuis]

Let's say C is your class, then C.prototype[Symbol.toStringTag] = C.name makes .toString() return '[object C]', and that works with v10.x and newer.

[nschonni]

Thanks, I'm trying to figure it out one the C/C++ side rather than the JS side

[bnoordhuis]

It's not much different, just more tedious. :-)

You get Symbol.toStringTag with v8::Symbol::GetToStringTag(isolate) and set it on the v8::FunctionTemplate::PrototypeTemplate() of your constructor callback.

[nschonni]

Thanks for the hints! I'll see what I can figure out