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

$ npm install --save @github/auto-check-element

Import as a modules:

import '@github/auto-check-element'

With a script tag:

<script type="module" src="./node_modules/@github/auto-check-element/dist/index.js">

<auto-check src="/signup-check/username" csrf="<%= authenticity_token_for("/signup-check/username") %>">
  <input>
</auto-check>

Note that in the following example the CSRF element is marked with the data-csrf attribute rather than name so that the value doesn't get posted to the backend when the element is placed in a form.

<auto-check src="/signup-check/username">
  <input>
  <input hidden data-csrf value="<%= authenticity_token_for("/signup-check/username") %>">
</auto-check>

• src is the server endpoint that will receive POST requests. The posted form contains a value parameter containing the text input to validate. Responding with a 200 OK status indicates the provided value is valid. Any other error status response indicates the provided value is invalid.
• csrf is the CSRF token for the posted form. It's available in the request body as a authenticity_token form parameter.
  • You can also supply the CSRF token via a child element. See usage example.
• required is a boolean attribute that requires the validation to succeed before the surrounding form may be submitted.

Request lifecycle events are dispatched on the <auto-check> element. These events do not bubble.

• loadstart - The server fetch has started.
• load - The network request completed successfully.
• error - The network request failed.
• loadend - The network request has completed.

Network events are useful for displaying progress states while the request is in-flight.

const check = document.querySelector('auto-check')
const container = check.parentElement
check.addEventListener('loadstart', () => container.classList.add('is-loading'))
check.addEventListener('loadend', () => container.classList.remove('is-loading'))
check.addEventListener('load', () => container.classList.add('is-success'))
check.addEventListener('error', () => container.classList.add('is-error'))

auto-check-start is dispatched on when there has been input in the element. In event.detail you can find:

• setValidity: A function to provide a custom failure message on the input. By default it is 'Verifying…'.

const input = check.querySelector('input')

input.addEventListener('auto-check-start', function(event) {
  const {setValidity} = event.detail
  setValidity('Loading validation')
})

auto-check-send is dispatched before the network request begins. In event.detail you can find:

• body: The FormData request body to modify before the request is sent.

const input = check.querySelector('input')

input.addEventListener('auto-check-send', function(event) {
  const {body} = event.detail
  body.append('custom_form_data', 'value')
})

auto-check-success is dispatched when the server responds with 200 OK. In event.detail you can find:

• response: The successful server Response. Its body can be used for displaying server-provided messages.

input.addEventListener('auto-check-success', async function(event) {
  const message = await event.detail.response.text()
  console.log('Validation passed', message)
})

auto-check-error is dispatched when the server responds with a 400 or 500 range error status. In event.detail you can find:

• response: The failed server Response. Its body can be used for displaying server-provided messages.
• setValidity: A function to provide a custom failure message on the input. By default it is 'Validation failed'.

input.addEventListener('auto-check-error', async function(event) {
  const {response, setValidity} = event.detail

  setValidity('Validation failed')

  const message = await response.text()
  console.log('Validation failed', message)
})

auto-check-complete is dispatched after either the success or error events to indicate the end of the auto-check lifecycle.

input.addEventListener('auto-check-complete', function(event) {
  console.log('Validation complete', event)
})

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.