new-js.html

<template>
  <div ref="content"> Hi! </div>
</template>

<script>
export default {
  name: "someComponent",
  data() {
    return {
      contentClass: ""
    },
    methods: {
      addClass(){
        return this.contentClass = "foo";
      }
    },
    mounted() {
      this.addClass();
    }
  }
}
</script>