EJSON should serialize Set and Map objects

[klaussner]

EJSON should serialize Set and Map objects so that they can be returned from methods and used as method arguments. This can be implemented in apps by adding the necessary functions to the Set and Map prototypes and adding custom EJSON types, but it would be nice to have that functionality by default:

import { Meteor } from 'meteor/meteor';
import { EJSON } from 'meteor/ejson';

Set.prototype.toJSONValue = function () {
  return Array.from(this);
};

Set.prototype.typeName = function () {
  return 'Set';
};

EJSON.addType('Set', (json) => {
  return new Set(json);
});

Meteor.methods({
  getSet() {
    const set = new Set;
    set.add('Meteor');
    set.add('❤️');

    return set;
  }
});

Related issue: meteor/meteor#8789 (@priyadarshy)

[luzlab]

I wrote this code for de/serializing Maps based on online sources.

import { Meteor } from 'meteor/meteor';
import { EJSON } from 'meteor/ejson';

Map.prototype.toJSONValue = function () {
  return JSON.stringify([...this]);
};

Map.prototype.typeName = function () {
  return 'Map';
};

EJSON.addType('Map', (jsonStr) => {
  return new Map(JSON.parse(jsonStr));
});

I'd make a PR if someone could suggest how to write it. I looked over the ejson code, but there doesn't seem to be an obvious place to add support for a custom type.