worker.send stripping Map and replacing with {}

[davebriand]

• Version:v6.9.4
• Platform:Darwin Daves-MacBook-Air-2.local 14.3.0 Darwin Kernel Version 14.3.0: Mon Mar 23 11:59:05 PDT 2015; root:xnu-2782.20.48~5/RELEASE_X86_64 x86_64
• Subsystem:

let worker = cluster.fork();
let myMap = new Map();
myMap.set('s', {foo: 'bar'});
worker.send({
  myMap: myMap
});

When the worker gets the message myMap becomes {}
When sending an array or object it works as expected

[cjihrig]

This is because send() calls JSON.stringify() on the Map. As a workaround, you can define a toJSON() method for your Map.

[TimothyGu]

Example solution that should work:

class SerializableMap extends Map {
  toJSON() {
    const obj = Object.create(null);
    for (const [key, value] of this) {
      obj[key] = value;
    }
    return obj;
  }
}

let worker = cluster.fork();
let myMap = new SerializableMap();
myMap.set('s', {foo: 'bar'});
worker.send({
  myMap
});

Other than that @cjihrig covered everything already, so closing.

[addaleax]

@TimothyGu are you okay with me reopening this? I’d like to see how far we can get with the ValueSerializer stuff once #11048 lands. (I’ll assign this issue to myself.)

[TimothyGu]

@addaleax no problem at all. Just trying to cleaning up some old and inactive issues.

[Trott]

@addaleax Is this still something you intend to look at? Or should this be closed?

[addaleax]

Yes, but it’s not something we can realistically do until V8 moves its API out of experimental status, I think (because this is about a non-experimental API of ours).

[BridgeAR]

Is this something we still want to pursue? In that case I guess it makes sense to add the help wanted label (I am not sure if the API is still experimental though but I hope not)?

[apapirovski]

@addaleax @TimothyGu Could you give a quick status update on this? I'm not familiar enough with V8 to know where this is at. Thank you!

[bnoordhuis]

Still experimental. There's also the issue that JSON is the documented serialization protocol so there might be applications or libraries out there relying on quirks of JSON.parse() and JSON.stringify().