var images = {

   "1": {

    id: "1",

    urls: ["/medium/1.jpg", "/large/1.jpg"]

   },

   "2": {

    id: "2",

    urls: ["/medium/1.jpg", "/large/1.jpg"]

   }

  };

​

var ImageRecord = Immutable.Record({ id: "0", urls: [] })

​

var imagesMap = Immutable.fromJS(images, function(key, value) {

  // This check should be replaced by a better way to know that

  // we really want image records

  if(/^[0-9]+$/.test(key)) {

    return new ImageRecord(value)

  }

  return value

});

​

// Verify that it's really a record

console.log(imagesMap.get("2").toJS())

console.log(imagesMap.get("2").delete("urls").toJS())