How to validate Vuetify text field asynchronously?

One solution is to set the error-messages prop:

<v-text-field v-model="input" :error-messages="errors">

and use the watch option:

new Vue({
  data () {
    return {
      input: '',
      errors: []
    }
  },
  watch: {
    input (val) {
        axios.get('/check?value=' + val).then(valid => {
          this.errors = valid ? [] : ['async error']
        })
    }
  }
});