diffCollection

diffCollection.js

function diffCollection(oldColl, newColl, key) {
  var oldVal = _.map(oldColl, function(model) {
    return model.get(key);
  });

  var newVal = _.map(newColl, function(model) {
    return model.get(key);
  });

  var changed = [];
  var removed = _.chain(oldColl).map(function(model) {
    if (_.indexOf(newVal, model.get(key)) === -1) {
      return model;
    } else {
      changed.push(model);
    }
  }).unique().value();

  var add = _.filter(newColl, function(model) {
    return _.indexOf(oldVal, model.get(key)) === -1;
  });

  return {
    add: add, 
    removed: removed, 
    changed: changed
  };
}

var collection = new MyCollection();
var currentData = [], lastData;

collection.on('reset', function(coll) {
  lastData = currentData;
  currentData = coll.models;

  var diff = diffCollection(lastData, currentData, 'hash');
  // diff data
  // update dem models
});

setInterval(function() {
  collection.fetch({ reset: true });
}, 10 * 1000);