willvalidate.js

import Vue from 'vue'

const clearErrors = form => {
    Array.from( form.querySelectorAll('.has-danger') ).map( el => el.classList.remove('has-danger') )
    Array.from( form.querySelectorAll('small') ).map( el => el.remove() )
}

const willvalidate = {

    install(Vue, options) {
        
        Vue.prototype.willvalidate = form => {

            clearErrors(form)
            let firstError=null
          
            Array.from( form ).map( field => {
                if (field.willValidate && !field.checkValidity()) 
                {
                  if (!firstError) firstError = field
                  const small     = document.createElement('small')
                  
                  if(field.getAttribute("errorMessage"))
                    small.innerHTML = field.getAttribute("errorMessage")
                  else 
                    small.innerHTML = field.validationMessage
                    
                  small.className = 'form-control-feedback'
                  field.parentElement.appendChild(small)
                  field.parentElement.classList.add('has-danger')
                } 
            })
        
            if (firstError) firstError.focus()
            return firstError === null

        }

    }
}
export default willvalidate