SOURCE

const myPlugin={
    install(Vue){
        Vue.mixin({
            created(){
                if(this.$options.rules){
                  Object.keys(this.$options.rules).forEach(key=>{
                      const rule=this.$options.rules[key]
                      this.$watch(key,newValue=>{
                          const result=rule.validate(newValue)
                          if(!result){
                              console.log(rule.message)
                          }
                      })
                  })  
                }
            }
        })
    }
}

const vm=new Vue({
    data:{foo:10},
    rules:{
        foo:{
            validate:value=>value>1,
            message:'foo must be greater than one'
        }
    }
})