Use transit-js Immutable.js with automatic conversion of plain JS objects to immutables

transit-immutable.js

var Transit = require('transit-js'),
    Imm = require('immutable');

// gil: It's possible that the following reader/writer configuration is incomplete.
//      This is a modified version of:
//      https://gist.github.com/Tvaroh/52efbe8f4541ca537908
//
// ... the original version of this utilized built-in JS (ES6?) types for
// better efficiency+speed. However, it didn't work with nested Map + OrderedMap.
// Improved efficiency+speed can be achieved by re-implementing with some native types.

var reader = Transit.reader('json', {
  // gil: I commented out arrayBuilder because it breaks OrderedMap handler.
  //      I think that this means that at the top-most level you can't have an array.
  //
  //arrayBuilder: {
  //  init: function () { return Imm.List.of().asMutable(); },
  //  add: function (ret, val) { return ret.push(val); },
  //  finalize: function (ret) { return ret.asImmutable(); },
  //  fromArray: function (arr) { return Imm.List(arr); }
  //},
  mapBuilder: {
    init: function () { return Imm.Map().asMutable(); },
    add: function (ret, key, val) { return ret.set(key, val);  },
    finalize: function (ret) { return ret.asImmutable(); }
  },
  handlers: {
    iL: function (arr) {
      return Imm.List(arr);
    },
    iS: function (arr) {
      return Imm.Set(arr);
    },
    iM: function (o) {
      return Imm.Map(o);
    },
    iOM: function (arr) {
      return Imm.OrderedMap(arr);
    }
  }
});

var writer = Transit.writer("json-verbose", {
  handlers: Transit.map([
    Imm.List, Transit.makeWriteHandler({
      tag: function () { return 'iL'; },
      rep: function (v) { return v.toArray(); },
      stringRep: function () { return null; }
    }),
    Imm.Map, Transit.makeWriteHandler({
      tag: function () { return 'iM'; },
      rep: function (v) { return v.toObject(); },
      stringRep: function () { return null; }
    }),
    Imm.Set, Transit.makeWriteHandler({
      tag: function () { return 'iS'; },
      rep: function (v) { return v.toArray(); },
      stringRep: function () { return null; }
    }),
    Imm.OrderedMap, Transit.makeWriteHandler({
      tag: function () { return 'iOM'; },
      rep: function (v) { return v.map(function(v,k) { return [k,v] } ).toArray() },
      stringRep: function () { return null; }
    })
  ])
});

module.exports = {

  toTransit: function (immutableValue) {
    return writer.write(immutableValue);
  },

  fromTransit: function (ts) {
    return reader.read(ts);
  }

};