Always serializes to Immutable.Map if multiple immutable libs are used

We’ve spent quite some time debugging one very strange issue. The effect was in Immutable.List being serialized and later de-serialized into Immutable.Map.

I will try to explain the problem as short as possible and suggest a solution at the end.

Summary

instanceof comparisons of transit-js fails to compare Immutable types if we have multiple immutable libraries used.

Explanation

We are using Lerna monorepo and all internal packages there are symlinked (the same effect can happen if you use npm link without doing work in monorepo at all)

Bootstrapped working project structure:

packages
  app
    node_modules
      immutable
      ->lib
  lib
    node_modules
      immutable

As you can see symlinked lib will also have its own immutable like:

packages
  app
    node_modules
      immutable
      ->lib
        node_modules
          immutable

  lib
    node_modules
      immutable

As soon as we export anything Immutable in lib and use it in app, trying to serialize the state would result in fallback to the default case of transit-immutable-js:

"default", transit.makeWriteHandler({
  tag: function() {
    return 'iM';
  }

The reason for that is transit-js tries to do a match by using instanceof and lib->Immutable.List does not match app->Immutable.List

Possible solution

Instead of passing a mapping of Immutable.X to transit-js always use default case and use native ImmutableJS methods like Immutable.List.isList(obj) to do matching.

We checked that in the app’s code and Immutable.List.isList(obj) works perfectly no matter what immutable is used there.

We did not check this on transit-immutable-js code yet. Need to see if it even possible (would be if transit-js somehow gives obj back to tag function of writeHandler

[jeffberry]

I had this same problem, I ended up figuring out it was because react native had it’s own instance of immutable installed in node_modules/react-native/node_modules/immutable. I was using a different version of Immutable in my app’s package.json; once I switched that version to the same version react-native requires (~3.7.6) the second installation in the react-native folder went away, and my issues were fixed. Thought this might be helpful to some.

[nkbt]

I actually wrote my owt transit library about 200 lines long that replaces both this one and whole transit-js. It is not hard especially if you are not trying to solve a one-fits-all usecase (not opensourse since we don’t want to support generic cases and just keep it focused on our own data sttuctures)

I need to find some time soon to backport part of its code here to solve this issue. It is actually pretty straightforward