Vue.js - access data from root instance within component

Question

This seems like a fairly basic question but I can't seem to find a definitive (or even working) answer.

I have my root instance:

var vm = new Vue({
  el: '#app',

  // Data
  data: {
      events: {}
  },

  // Methods
  methods: {

    fetchEvents: function(){
      this.$http.get('/api/events').success(function(theseEvents) {
      this.$set('events', theseEvents);

      }).error(function(error) {

      });

    }
},

ready: function(){

  this.fetchEvents();

}

});

And I have a separate component in which I want to list out the events that are stored in the root instance. At the moment it looks like this:

var EventsList = Vue.extend({

template: '<ul><li v-for="event in events"><h2>{{ event.title }}</h2><p>{{ event.body }}</p></li></ul>',

data: function(){
  return {
    events: {}
  }
},

methods: {

  syncEvents: function(){
    this.$set('events', this.$parent.events);
  }

},

// When ready...
ready: function(){
  this.syncEvents();
}
}

This doesn't seem to work. I have also tried this.$root.events to no avail. What is the correct way to go about this? Bear in mind I want to reference the data from the root, not create a copy with its own scope.

EDIT: trying to use props, here is the list component, which is also not working:

var EventsList = Vue.extend({

template: '<ul><li v-for="event in events"><h2>{{ event.title }}</h2><p>{{ event.body }}</p></li></ul>',

props: ['events']

}

Answer 1

Using props, you can easily pass the same data from parent to children. Since I don't know how you linked the root instance and the EventList together, I'm going to assume you registered it as a global component.

The documentation states:

Note that if the prop being passed down is an Object or an Array, it is passed by reference. Mutating the Object or Array itself inside the child will affect parent state, regardless of the binding type you are using.

So you will be using the same object throughout all your components when you pass it as a prop.

var vm = new Vue({
  el: '#app',

  // Data
  data: {
      events: {}
  },

  // Methods
  methods: {

    fetchEvents: function(){
      this.$http.get('/api/events').success(function(theseEvents) {
      this.$data.events = theseEvents; // You don't need to use $set here

      }).error(function(error) {

      });

    }
},

ready: function(){

  this.fetchEvents();

}

});

EventList:

var EventsList = Vue.extend({

template: '<ul><li v-for="event in events"><h2>{{ event.title }}</h2><p>{{ event.body }}</p></li></ul>',

data: function(){
  return {
  }
},
props: {
    events: Object, // assuming that your prop is an object
},
}

// Register the vue component globally, if you want to:
Vue.component('eventlist', EventsList);

In the root vue instance template, you can pass the root vue instances events as a property called events in the child component:

<div class="app">
    <!-- events is passed using the :events prop -->
    <eventlist :events="events">
    </eventlist>
</div>

Answer 2

That's what "Props" are for:

http://vuejs.org/guide/components.html#Props

If you pass an object/array as a prop (what your events data will surely be), it's two-way syncing automatically - change events in the child, they are changed in the parent.

If you pass simple values (strings, numbers - e.g. only event.name) via props, you have to explicitly use the .sync modifier: http://vuejs.org/guide/components.html#Prop_Binding_Types