ractivejs observe init vs set/push/update

Question

in this code sample, on init, observe is fired for each element, even ones without "prices", but does not fire on any other method, Why?

var _deals = [
    {
        prices: [
            {
                id: 1,
                deal_id: 1,
                guests_from: 100,
                guests_to: 200,
                price: 250
            }
        ]
    },
    {
        prices: []
    },
    {}  // this fires also, Why?
];


var deals = [], // app database
    dealsGuy;   // app instance


deals = _deals;


// create our app view

dealsGuy = new Ractive({
  el: '#app_block',
  template: '#app-template',
  noIntro: true, // disable transitions during initial render

  data: {
    deals: deals
  },

  decorators: {
    datepicker: datepickerDecorator
  }
});   

dealsGuy.observe('deals.*.prices', function (newValue, oldValue, keypath) {

    console.log( 'observe', keypath );

    if( newValue === void 0 || newValue.length <= 0 ){

        this.set(keypath,[{}]);
    }
});

dealsGuy.push('deals', {}); // does not fire 'deals.*.prices'

Answer 1

I guess it's due to a subbtle difference how things are considered during initialization and updates.

The initialization observe is always triggered (even if the value is undefined ), while updates are only triggerred if the value actually changes.