How to get index of selected option with vue.js

Question

Sorry for newbie question. But how can i get an index of selected element from selectbox and run a function. My code below doesn't trigger switchView() function.

<select id="selectbox" @change="switchView(index)">
  <option [v-for="(item, index) in items" v-bind:value="item.title"]>
    {{ item.title }}
  </option>
</select>

any help will be appreciated.

EDITED: moved @change="switchView(index)" from <option> to <select>, thanks to @Phil

I need index, because i have several calculated items. And i need change view according to user's selection from items.

Answer 1

Pass $event.target.selectedIndex to your function

Use the @change directive to listen to the change event. Invoke your function and pass the $event or the selected index of the event target $event.target.selectedIndex as a parameter to your function.

<select @change="switchView($event, $event.target.selectedIndex)">

Your method receives the passed parameters.

  methods: {
    switchView: function(event, selectedIndex) {
      console.log(event, selectedIndex);
    }
  }

Full Example https://jsfiddle.net/3p7rhjyw/

<div id="app">
  <select @change="switchView($event, $event.target.selectedIndex)">
  <option v-for="(item, index) in items" v-bind:value="item.title">
    {{ item.title }}
  </option>
</select> 
<p>
{{ selectedIndex }} {{ items[selectedIndex].id }}
</p>
</div>

<script>
new Vue({
  el: "#app",
  data: {
    items: [
      { title: "Learn JavaScript", id: 'A' },
      { title: "Learn Vue", id: 'B' },      
      { title: "Play around in JSFiddle", id: 'C' },
      { title: "Build something awesome", id: 'D' }
    ],
    selectedIndex: 0
  },
  methods: {
    switchView: function(event, selectedIndex) {
      console.log(event, selectedIndex);      
      this.selectedIndex = selectedIndex;
    }
  }
});
</script>

Mozilla documentation about HTMLSelectElement.selectedIndex.

Answer 2

For an pre-modified bootstrap-vue, this event handling might be different from the $event.target.selectedIndex. Especially for Vue 3, this answer might save your time.

<b-form-select @change="onChange" :options="options"></b-form-select>

Method that receives event from the user selection.

  methods: {
    onChange: function(event) {
      let index = event.target.selectedIndex
    }
  }

Full Example might be as follows:

<div id="app">
  <select @change="onChange">
  </select> 
  <p>Selected index: {{ selectedIndex }}</p>
</div>

<script>
new Vue({
  el: "#app",
  data: {
    items: [
      "option 1",
      "option 2",
      "option 3",
      "option 4"
    ],
    selectedIndex: 0
  },
  methods: {
     onChange: function(event) {
       let index = event.target.selectedIndex // this selectedIndex is from event.
       this.selectedIndex = index
     }
  }
});
</script>