Experimenting with "firstChange" event in Ember

first-change.js

var onNextChange = function(model, handler, context) {
  var fields = Ember.get(model.constructor, 'fields').keys.toArray();
  // Avoid multiple invocations from batched changes using a boolean guard.
  var hasChanged = false;
  var handleChange = function() {
    if (hasChanged) {
      return;
    }
    hasChanged = true;

    fields.forEach(function(field) {
      model.removeObserver(field, null, handleChange);
    });

    handler.call(context || this);
  };
  fields.forEach(function(field) {
    model.addObserver(field, null, handleChange);
  });
};


// usage:

var BMac = DS.Model.extend({
  setupWasModified: function() {
    this.set('wasModified', false);
    onNextChange(this, function() {
      this.set('wasModified', true);
    }, this);
  }.on('init')
});