Vuetify 表單規則驗證

Vuetify component:

<v-text-field :rules="[ sellerId ]"></v-text-field>

JS：

data: function () {
  return {
    disabled: false
  }
},
methods: { 
  sellerId (value) {
    if (value.length === 0) {
      this.disabled = true;
      return "What are you trying to do here?";  
    } else {
      return true;
    }
  }
}