Console log WeakSet and WeakMap always empty

[anantoghosh]

• Version: 8.9.4
• Platform: Windows 10 x64
• Subsystem: powershell

Currently trying to console.log WeakSet or WeakMap will always display as empty.

var set = new WeakSet([{yes: true}]);
console.log(set); // logs WeakSet{}

var map = new WeakMap([[{yes: true}, true]]);
console.log(map); // logs WeakMap{}

I believe I understand why logging them does not work, but node should display a warning and/or should document this behavior.

[devsnek]

related to #18227

[BridgeAR]

This is language related and it is just not possible to inspect WeakSet / WeakMap.

We did not yet come to a conclusion how to handle this on the long term and I am going to write a summary of pro / con some time this week.

@anantoghosh what kind of warning would you expect? I can not think of a good way to display a warning in this case.

[anantoghosh]

what kind of warning would you expect?

Maybe a message after using console.log()
"WARNING: WeakSet/WeakMap will always appear empty. See link"

Although simply mentioning this in the documentation would have been fine.
Currently, trying to google for this issue does not reveal any information.

[bnoordhuis]

This is language related and it is just not possible to inspect WeakSet / WeakMap.

At least w.r.t. inspection it should be possible to add a V8 API to peek into them.

In fact, it already exists but not in any official capacity:

$ ./out/Release/node --allow_natives_syntax
> var m = new WeakMap()
undefined

> m.set({x:1}, true);
WeakMap {}

> %GetWeakMapEntries(m, 99)
[ { x: 1 }, true ]

[BridgeAR]

@bnoordhuis that is a very interesting point and opens new possibilities for the other discussion as well. The question for me though is: can this be implemented independent of the engine?

[BridgeAR]

Support for inspecting WeakMap and WeakSet was added in master. The showHidden option must be set to true and otherwise it will tell that the items were not inspected.