const app = Vue.createApp({
  data() {
    return {
      title:'',
      tabs: [  
        {link:'', name: "Sec 1", dropdown: false, dropdownTabs:[]},
        {link:'', name: "Sec 2", dropdown: false, dropdownTabs:[]}
      ]
    }
  },
  methods: {
    getTabTitle(title) {
      console.log(title)
      this.title =title
    }
  }
})
app.component('topbar', {
  template: `
    <div v-for="(tab, i) in tabs" :key="i">
      <button @click="send(tab.name)">{{ tab.name }}</button>
    </div>
  `,
  props: ['tabs'],
  methods: {
    send(title) {
      this.$emit('passData', title)
    }
  }
})
app.mount('#demo')

<script src="https://unpkg.com/vue@3/dist/vue.global.prod.js"></script>
<div id="demo">
  <b>{{ title }}</b>
  <topbar :tabs='tabs' @pass-data="getTabTitle"></topbar>
</div>