JSFiddle - React, Tailwind, and code Playground

HTML

<div id="app">
  <div v-for="ref in refs">
    {{collapse_id(ref)}}
  </div>

</div>

JavaScript

new Vue({
  el: '#app',
  methods: {
    collapse_id(thread_ref) {
      return 'collapse_' + thread_ref
    }
  },
  data: {
    refs: [123, 234, 345]
  }
})