auto-check-element | Vaadin

An input element that validates its value with a server endpoint.

<auto-check> element

An input element that validates its value against a server endpoint.


$ npm install --save auto-check-element


import 'auto-check-element'
<auto-check src="/signup_check/username" csrf="<%= authenticity_token_for("/signup_check/username") %>">

Provide a URL and a CSRF token and the autocheck component will show validation confirmations and validation errors.

The endpoint should respond to POST requests with:

  • a 200 HTTP status code if the provided value if valid.
  • a 422 HTTP status code if the provided value is invalid.
  • a optional error message in the body and a Content-Type header with a value of text/html; fragment.


const check = document.querySelector('auto-check')

// Network request lifecycle events.
check.addEventListener('loadstart', function(event) {
  console.log('Network request started', event)
check.addEventListener('loadend', function(event) {
  console.log('Network request complete', event)
check.addEventListener('load', function(event) {
  console.log('Network request succeeded', event)
check.addEventListener('error', function(event) {
  console.log('Network request failed', event)

// Auto-check result events.
const input = check.querySelector('input')

input.addEventListener('auto-check-send', function(event) {
  console.log('Adding to FormData before network request is sent.')
  const {body} = event.detail
  body.append('custom_form_data', 'value')
input.addEventListener('auto-check-success', function(event) {
  const {message} = event.detail
  console.log('Validation passed', message)
input.addEventListener('auto-check-error', function(event) {
  const {message} = event.detail
  console.log('Validation failed', message)
input.addEventListener('auto-check-complete', function(event) {
  console.log('Validation complete', event)

Browser support

Browsers without native custom element support require a polyfill.

  • Chrome
  • Firefox
  • Safari
  • Microsoft Edge


npm install
npm test


Distributed under the MIT license. See LICENSE for details.


Link to this version
ImportedReleased 26 April 2019MIT License
Framework Support
Browser Independent
Install with
npm install auto-check-element"@2.0.0"
Run the above npm command in your project folder. If you have any issues installing, please contact the author.
Release notes - Version 2.0.0