Vue Component within Vue Component, scopes seem to be conflicting

Question

I have got a simple dropdown component, which simply allows me to hide and display some HTML, it's very basic.

However if I use this same component within itself, clicking the Test 2 dropdown toggle will collapse the first dropdown...

<dropdown>
    <li slot-scope="{ display, toggleDisplay }" @click="toggleDisplay()" :class="{ active: display }">
        Test
        <ul>
            <dropdown>
                <li slot-scope="{ display, toggleDisplay }" @click="toggleDisplay()" :class="{ active: display }">
                    Test 2
                </li>
            </dropdown>
        </ul>
    </li>
</dropdown>

Why is this? Also, I should be able to just do display = !display within the click event to toggle it rather than a function?

The component:

<script>
    export default {
        props: [ 'expanded' ],
        data: function() {
            return {
                display: !!(this.expanded)
            }
        },
        render() {
            return this.$scopedSlots.default({
                display: this.display,
                toggleDisplay: this.toggleDisplay
            })
        },
        methods: {
            toggleDisplay() {
                this.display = !this.display;
            }
        }
    }
</script>

Answer 1

This is called event bubbling(https://javascript.info/bubbling-and-capturing) and to prevent it use stopPropagation();.

I've removed the brackets (@click="toggleDisplay") to set $event automatically. You can also write: @click="toggleDisplay($event)".

Vue.component("dropdown", {
    props: ["expanded"],
    data: function() {
        return {
            display: !!this.expanded
        };
    },
    render() {
        return this.$scopedSlots.default({
            display: this.display,
            toggleDisplay: this.toggleDisplay
        });
    },
    methods: {
        toggleDisplay(e) {
            e.stopPropagation(); // this line
            this.display = !this.display;
        }
    }
});

new Vue().$mount("#app");

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.10/vue.js"></script>

<div id="app">
  <dropdown>
    <li slot-scope="{ display, toggleDisplay }" @click="toggleDisplay" :class="{ active: display }">
      {{ display }}
      Test
      <ul>
        <dropdown>
          <li slot-scope="{ display, toggleDisplay }" @click="toggleDisplay" :class="{ active: display }">
            {{ display }}
            Test 2
          </li>
        </dropdown>
      </ul>
    </li>
  </dropdown>
</div>