fromJS() only works on Objects in the same Realm

[gajus]

How to reproduce

const Immutable = require('immutable');
const vm = require('vm');

console.log('OUT', Immutable.Iterable.isIterable(Immutable.fromJS({})) );

vm.runInNewContext(`
  console.log('IN', Immutable.Iterable.isIterable(Immutable.fromJS({})) );
`, {
  console,
  Immutable
}, {});

Output

OUT true
IN false

Expected output

OUT true
IN true

[gajus]

It all comes down to value.constructor === Object in /src/fromJS.js#L39. Outside of the VM it executes to true and inside the VM it executes to false.

I have tried adding Object to the sandbox, but it didn't change the outcome.

[gajus]

Even this doesn't work:

const vm = require('vm');

vm.runInNewContext(`
  const Immutable = require('immutable');

  console.log( Immutable.Iterable.isIterable(Immutable.fromJS({})) );
`, {
  console,
  require,
});

[gajus]

Interesting to note that the following evaluates to true:

const vm = require('vm');

vm.runInNewContext(`
  console.log( test.constructor === Object );

`, {
  console,
  test: {},
  Object
});

which is expected, and would seem to indicate that Immutable.js plain object check should work too.

[gajus]

Oh, I see:

const vm = require('vm');

vm.runInNewContext(`
  console.log( {}.constructor === Object );
`, {
  console,
  Object
});

This evaluates to false. Thats explain why. Not sure how to fix it, though.

[gajus]

@leebyron Is there any interest in getting this fixed?

[leebyron]

For sure. #1056 is one attempt, however it has some punishing performance qualities.

I'm open to more exploration on this topic

[turnerhayes]

I suspect this is what's causing my custom REPL (using the REPL module) to exhibit the same issue--presumably, the REPL module is using a VM under the hood. Using the regular Node REPL (i.e. just invoking node on the command line) doesn't have this issue.

[turnerhayes]

Although when I run ({x: 1}).constructor === Object from within my custom REPL, it returns true, which sounds contrary to the diagnosis here, but maybe there's some weirdness around closures or something.