FormElement.vue

<template>
  <div class="form-element">
    <div>{{ field.title }}</div>

    <slot :value="field.value" :update="update"></slot>

    <div v-if="empty" class="empty">Must not be empty</div>
  </div>
</template>

<script>
export default {
  props: {
    field: {
      type: Object,
      default: () => {}
    },
  },

  computed: {
    empty() {
      if (this.field.value) {
        return this.field.value.length === 0
      }
      return true
    }
  },

  methods: {
    update(event) {
      this.field.value = event.target.value
    }
  }
}
</script>

<style scoped>
.form-element {
  margin-bottom: 1rem
}
.empty {
  color: red
}
</style>