AJAX & Async Requests·AJAX from first request to live updates

Forms without a reload

Submit forms with fetch and render field errors.

Beginner 13 min read Lesson 5 of 300 Challenge included

What you will be able to do

Use event.preventDefault().
Use FormData for multipart submissions.
Render field errors next to inputs.
Re-enable the submit button in finally.

In plain English

Intercept submit, build FormData, send it and render the server response. Keep native validation as a convenience, but always send the data to the server for real validation.

form.jsJavaScript

form.addEventListener('submit', async (event) => {
  event.preventDefault()
  const button = form.querySelector('button')
  button.disabled = true
  try {
    const response = await fetch('/api/signup', { method: 'POST', body: new FormData(form) })
    if (!response.ok) throw new Error('Save failed')
  } finally {
    button.disabled = false
  }
})

Your turn

Prevent the reload

Easy

Stop the default submit event.

JAVASCRIPT · starter

form.addEventListener('submit', (event) => {

Check your understanding before moving on.

Knowledge checkQuestion 1

Which API builds a multipart body from a form?

Select an answer to continue

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Lesson 5 of 300 · 0% of course