update model from custom directive VueJS
<p>I currently use Vue.JS 2.0 and I want to update the model off one Vue instance from an custom directive, but im looking a nice way to do it, this is because i trying to create an custom directive that implement JQueryUI-Datepicker the code is the follow:</p>

<pre><code>&lt;input type="text" v-datepicker="app.date" readonly="readonly"/&gt;

Vue.directive('datepicker', {
  bind: function (el, binding) {
    $(el).datepicker({
      onSelect: function (date) {
        //this is executed every time i choose an date from datepicker
        //pop.app.date = date; //this work find but is not dynamic to parent and is very dirty
        Vue.set(pop, binding.expression, date); //this should work but nop
      }
    });
  },
  update: function (el, binding) {
    $(el).datepicker('setDate', binding.value);
  }
});

var pop = new Vue({
    el: '#popApp',
    data: {
        app: {
            date: ''
        }
    }
});
</code></pre>

<p>Someone know how to update pop.app.date in a dynamic way from the directive, i know that binding.expression return in this example app.date and date return the current date picked in the datepicker but i dont know how to update the model from the directive</p>