Triggering HTML5 Form Validation

Question

I have a form with several different fieldsets. I have some Javascript that displays the field sets to the users one at a time. For browsers that support HTML5 validation, I'd love to make use of it. However, I need to do it on my terms. I'm using JQuery.

When a user clicks a JS Link to move to the next fieldset, I need the validation to happen on the current fieldset and block the user from moving forward if there is issues.

Ideally, as the user loses focus on an element, validation will occur.

Currently have novalidate going and using Javascript. Would prefer to use the native method. :)

Answer 1

TL;DR: Not caring about old browsers? Use form.reportValidity().

Need legacy browser support? Read on.

---

It actually is possible to trigger validation manually.

I'll use plain JavaScript in my answer to improve reusability, no jQuery is needed.

---

Assume the following HTML form:

<form>
  <input required>
  <button type="button">Trigger validation</button>
</form>

And let's grab our UI elements in JavaScript:

var form = document.querySelector('form')
var triggerButton = document.querySelector('button')

---

Don't need support for legacy browsers like Internet Explorer? This is for you.

All modern browsers support the reportValidity() method on form elements.

triggerButton.onclick = function () {
    form.reportValidity()
}

That's it, we're done. Also, here's a simple CodePen using this approach.

---

Approach for older browsers

Below is a detailed explanation how reportValidity() can be emulated in older browsers.

However, you don't need to copy&paste those code blocks into your project yourself — there is a ponyfill/polyfill readily available for you.

Where reportValidity() is not supported, we need to trick the browser a little bit. So, what will we do?

1. Check validity of the form by calling form.checkValidity(). This will tell us if the form is valid, but not show the validation UI.
2. If the form is invalid, we create a temporary submit button and trigger a click on it. Since the form is not valid, we know it won't actually submit, however, it will show validation hints to the user. We'll remove the temporary submit button immedtiately, so it will never be visible to the user.
3. If the form is valid, we don't need to interfere at all and let the user proceed.

---

In code:

triggerButton.onclick = function () {
  // Form is invalid!
  if (!form.checkValidity()) {
    // Create the temporary button, click and remove it
    var tmpSubmit = document.createElement('button')
    form.appendChild(tmpSubmit)
    tmpSubmit.click()
    form.removeChild(tmpSubmit)

  } else {
    // Form is valid, let the user proceed or do whatever we need to
  }
}

This code will work in pretty much any common browser (I've tested it successfully down to IE11).

Here's a working CodePen example.