Principe

Possibilité de customiser les éléments de validation des formulaires.

La validation des formulaires HTML se fait en utilisant les pseudo-classes :invalid et :valid et s'applique aux éléments input, select et textarea.
Bootstrap limite la portée à la classe parente .was-validated appliquée généralement sur le balise form.

Custom Style

Pour personnaliser les messages de validation via Bootstrap, ajouter novalidate sur la balise form.
Cela désactive les infobulles par défaut du navigateur.
Lors de la soumission, les :invalid et :valid sont appliqués aux éléments de formulaire.

Les styles de feedback personnalisés appliquent les couleurs, bordures, styles de focus, icônes.

Looks good!
Looks good!
@
Please choose a username.
Please provide a valid city.
Please select a valid state.
Please provide a valid zip.
You must agree before submitting. 
<form class="row g-3 needs-validation" novalidate>
    <div class="col-md-4">
        <label for="validationCustom01" class="form-label">First name</label>
        <input type="text" class="form-control" id="validationCustom01" value="Mark" required>
        <div class="valid-feedback">
            Looks good!
        </div>
    </div>
    <div class="col-md-4">
        <label for="validationCustom02" class="form-label">Last name</label>
        <input type="text" class="form-control" id="validationCustom02" value="Otto" required>
        <div class="valid-feedback">
            Looks good!
        </div>
    </div>
    <div class="col-md-4">
        <label for="validationCustomUsername" class="form-label">Username</label>
        <div class="input-group has-validation">
            <span class="input-group-text" id="inputGroupPrepend">@</span>
            <input type="text" class="form-control" id="validationCustomUsername" aria-describedby="inputGroupPrepend" required>
            <div class="invalid-feedback">
                Please choose a username.
            </div>
        </div>
    </div>
    <div class="col-md-6">
        <label for="validationCustom03" class="form-label">City</label>
        <input type="text" class="form-control" id="validationCustom03" required>
        <div class="invalid-feedback">
            Please provide a valid city.
        </div>
    </div>
    <div class="col-md-3">
        <label for="validationCustom04" class="form-label">State</label>
        <select class="form-select" id="validationCustom04" required>
            <option selected disabled value="">Choose...</option>
            <option>...</option>
        </select>
        <div class="invalid-feedback">
            Please select a valid state.
        </div>
    </div>
    <div class="col-md-3">
        <label for="validationCustom05" class="form-label">Zip</label>
        <input type="text" class="form-control" id="validationCustom05" required>
        <div class="invalid-feedback">
            Please provide a valid zip.
        </div>
    </div>
    <div class="col-12">
        <div class="form-check">
            <input class="form-check-input" type="checkbox" value="" id="invalidCheck" required>
            <label class="form-check-label" for="invalidCheck">Agree to terms and conditions</label>
            <div class="invalid-feedback">
                You must agree before submitting.
            </div>
        </div>
    </div>
    <div class="col-12">
        <button class="btn btn-primary" type="submit">Submit form</button>
    </div>
</form>

Et côté JS :

// Example starter JavaScript for disabling form submissions if there are invalid fields
(() => {
  'use strict'

  // Fetch all the forms we want to apply custom Bootstrap validation styles to
  const forms = document.querySelectorAll('.needs-validation')

  // Loop over them and prevent submission
  Array.from(forms).forEach(form => {
    form.addEventListener('submit', event => {
      if (!form.checkValidity()) {
        event.preventDefault()
        event.stopPropagation()
      }

      form.classList.add('was-validated')
    }, false)
  })
})()
Navigateur par défaut

Essayez de valider le formulaire ci-dessous pour constater le comportement par défaut d'un formulaire.

@ 
<form class="row g-3">
    <div class="col-md-4">
        <label for="validationDefault01" class="form-label">First name</label>
        <input type="text" class="form-control" id="validationDefault01" value="Mark" required>
    </div>
    <div class="col-md-4">
        <label for="validationDefault02" class="form-label">Last name</label>
        <input type="text" class="form-control" id="validationDefault02" value="Otto" required>
    </div>
    <div class="col-md-4">
        <label for="validationDefaultUsername" class="form-label">Username</label>
        <div class="input-group">
            <span class="input-group-text" id="inputGroupPrepend2">@</span>
            <input type="text" class="form-control" id="validationDefaultUsername" aria-describedby="inputGroupPrepend2" required>
        </div>
    </div>
    <div class="col-md-6">
        <label for="validationDefault03" class="form-label">City</label>
        <input type="text" class="form-control" id="validationDefault03" required>
    </div>
    <div class="col-md-3">
        <label for="validationDefault04" class="form-label">State</label>
        <select class="form-select" id="validationDefault04" required>
            <option selected disabled value="">Choose...</option>
            <option>...</option>
        </select>
    </div>
    <div class="col-md-3">
        <label for="validationDefault05" class="form-label">Zip</label>
        <input type="text" class="form-control" id="validationDefault05" required>
    </div>
    <div class="col-12">
        <div class="form-check">
            <input class="form-check-input" type="checkbox" value="" id="invalidCheck2" required>
            <label class="form-check-label" for="invalidCheck2">Agree to terms and conditions</label>
        </div>
    </div>
    <div class="col-12">
        <button class="btn btn-primary" type="submit">Submit form</button>
    </div>
</form>
Côté serveur

En cas de besoin d'une validation côté serveur, il est possible de jouer avec .is-invalid et .is-valid.
Notez que .invalid-feedback est également pris en charge.
Pour les champs invalides, assurez-vous que le message est associé au champ de formulaire concerné via aria-describedby.
Pour corriger certains effets de bord sur les border-radius, les groupes nécessitent la classe .has-validation.

Looks good!
Looks good!
@
Please choose a username.
Please provide a valid city.
Please select a valid state.
Please provide a valid zip.
You must agree before submitting. 
<form class="row g-3">
    <div class="col-md-4">
        <label for="validationServer01" class="form-label">First name</label>
        <input type="text" class="form-control is-valid" id="validationServer01" value="Mark" required>
        <div class="valid-feedback">
            Looks good!
        </div>
    </div>
    <div class="col-md-4">
        <label for="validationServer02" class="form-label">Last name</label>
        <input type="text" class="form-control is-valid" id="validationServer02" value="Otto" required>
        <div class="valid-feedback">
            Looks good!
        </div>
    </div>
    <div class="col-md-4">
        <label for="validationServerUsername" class="form-label">Username</label>
        <div class="input-group has-validation">
            <span class="input-group-text" id="inputGroupPrepend3">@</span>
            <input type="text" class="form-control is-invalid" id="validationServerUsername" aria-describedby="inputGroupPrepend3 validationServerUsernameFeedback" required>
            <div id="validationServerUsernameFeedback" class="invalid-feedback">
                Please choose a username.
            </div>
        </div>
    </div>
    <div class="col-md-6">
        <label for="validationServer03" class="form-label">City</label>
        <input type="text" class="form-control is-invalid" id="validationServer03" aria-describedby="validationServer03Feedback" required>
        <div id="validationServer03Feedback" class="invalid-feedback">
            Please provide a valid city.
        </div>
    </div>
    <div class="col-md-3">
        <label for="validationServer04" class="form-label">State</label>
        <select class="form-select is-invalid" id="validationServer04" aria-describedby="validationServer04Feedback" required>
            <option selected disabled value="">Choose...</option>
            <option>...</option>
        </select>
        <div id="validationServer04Feedback" class="invalid-feedback">
            Please select a valid state.
        </div>
    </div>
    <div class="col-md-3">
        <label for="validationServer05" class="form-label">Zip</label>
        <input type="text" class="form-control is-invalid" id="validationServer05" aria-describedby="validationServer05Feedback" required>
        <div id="validationServer05Feedback" class="invalid-feedback">
            Please provide a valid zip.
        </div>
    </div>
    <div class="col-12">
        <div class="form-check">
            <input class="form-check-input is-invalid" type="checkbox" value="" id="invalidCheck3" aria-describedby="invalidCheck3Feedback" required>
            <label class="form-check-label" for="invalidCheck3">Agree to terms and conditions</label>
            <div id="invalidCheck3Feedback" class="invalid-feedback">
                You must agree before submitting.
            </div>
        </div>
    </div>
    <div class="col-12">
        <button class="btn btn-primary" type="submit">Submit form</button>
    </div>
</form>
Éléments pris en charge
  • input et textarea avec .form-control
  • select avec .form-select
  • .form-check
Please enter a message in the textarea.
Example invalid feedback text
More example invalid feedback text
Example invalid select feedback
Example invalid form file feedback 
<form class="was-validated">
    <div class="mb-3">
        <label for="validationTextarea" class="form-label">Textarea</label>
        <textarea class="form-control" id="validationTextarea" placeholder="Required example textarea" required></textarea>
        <div class="invalid-feedback">
            Please enter a message in the textarea.
        </div>
    </div>

    <div class="form-check mb-3">
        <input type="checkbox" class="form-check-input" id="validationFormCheck1" required>
        <label class="form-check-label" for="validationFormCheck1">Check this checkbox</label>
        <div class="invalid-feedback">
            Example invalid feedback text
        </div>
    </div>

    <div class="form-check">
        <input type="radio" class="form-check-input" id="validationFormCheck2" name="radio-stacked" required>
        <label class="form-check-label" for="validationFormCheck2">Toggle this radio</label>
    </div>
    <div class="form-check mb-3">
        <input type="radio" class="form-check-input" id="validationFormCheck3" name="radio-stacked" required>
        <label class="form-check-label" for="validationFormCheck3">Or toggle this other radio</label>
        <div class="invalid-feedback">
            More example invalid feedback text
        </div>
    </div>

    <div class="mb-3">
        <select class="form-select" required aria-label="select example">
            <option value="">Open this select menu</option>
            <option value="1">One</option>
            <option value="2">Two</option>
            <option value="3">Three</option>
        </select>
        <div class="invalid-feedback">
            Example invalid select feedback
        </div>
    </div>

    <div class="mb-3">
        <input type="file" class="form-control" aria-label="file example" required>
        <div class="invalid-feedback">
            Example invalid form file feedback
        </div>
    </div>

    <div class="mb-3">
        <button class="btn btn-primary" type="submit" disabled>Submit form</button>
    </div>
</form>
Infobulles

Sous réserve d'avoir une position relative sur les éléments parents, il est possible de skinner les validations de formulaire via des infobulles (sorte de tooltips).

Looks good!
Looks good!
@
Please choose a unique and valid username.
Please provide a valid city.
Please select a valid state.
Please provide a valid zip. 
<form class="row g-3 needs-validation" novalidate>
    <div class="col-md-4 position-relative">
        <label for="validationTooltip01" class="form-label">First name</label>
        <input type="text" class="form-control" id="validationTooltip01" value="Mark" required>
        <div class="valid-tooltip">
            Looks good!
        </div>
    </div>
    <div class="col-md-4 position-relative">
        <label for="validationTooltip02" class="form-label">Last name</label>
        <input type="text" class="form-control" id="validationTooltip02" value="Otto" required>
        <div class="valid-tooltip">
            Looks good!
        </div>
    </div>
    <div class="col-md-4 position-relative">
        <label for="validationTooltipUsername" class="form-label">Username</label>
        <div class="input-group has-validation">
            <span class="input-group-text" id="validationTooltipUsernamePrepend">@</span>
            <input type="text" class="form-control" id="validationTooltipUsername" aria-describedby="validationTooltipUsernamePrepend" required>
            <div class="invalid-tooltip">
                Please choose a unique and valid username.
            </div>
        </div>
    </div>
    <div class="col-md-6 position-relative">
        <label for="validationTooltip03" class="form-label">City</label>
        <input type="text" class="form-control" id="validationTooltip03" required>
        <div class="invalid-tooltip">
            Please provide a valid city.
        </div>
    </div>
    <div class="col-md-3 position-relative">
        <label for="validationTooltip04" class="form-label">State</label>
        <select class="form-select" id="validationTooltip04" required>
            <option selected disabled value="">Choose...</option>
            <option>...</option>
        </select>
        <div class="invalid-tooltip">
            Please select a valid state.
        </div>
    </div>
    <div class="col-md-3 position-relative">
        <label for="validationTooltip05" class="form-label">Zip</label>
        <input type="text" class="form-control" id="validationTooltip05" required>
        <div class="invalid-tooltip">
            Please provide a valid zip.
        </div>
    </div>
    <div class="col-12">
        <button class="btn btn-primary" type="submit">Submit form</button>
    </div>
</form>
CSS
Variables SASS
$form-feedback-margin-top:          $form-text-margin-top;
$form-feedback-font-size:           $form-text-font-size;
$form-feedback-font-style:          $form-text-font-style;
$form-feedback-valid-color:         $success;
$form-feedback-invalid-color:       $danger;

$form-feedback-icon-valid-color:    $form-feedback-valid-color;
$form-feedback-icon-valid:          url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 8 8'><path fill='#{$form-feedback-icon-valid-color}' d='M2.3 6.73.6 4.53c-.4-1.04.46-1.4 1.1-.8l1.1 1.4 3.4-3.8c.6-.63 1.6-.27 1.2.7l-4 4.6c-.43.5-.8.4-1.1.1'/></svg>");
$form-feedback-icon-invalid-color:  $form-feedback-invalid-color;
$form-feedback-icon-invalid:        url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 12 12' width='12' height='12' fill='none' stroke='#{$form-feedback-icon-invalid-color}'><circle cx='6' cy='6' r='4.5'/><path stroke-linejoin='round' d='M5.8 3.6h.4L6 6.5z'/><circle cx='6' cy='8.2' r='.6' fill='#{$form-feedback-icon-invalid-color}' stroke='none'/></svg>");
$form-valid-color:                  $form-feedback-valid-color;
$form-valid-border-color:           $form-feedback-valid-color;
$form-invalid-color:                $form-feedback-invalid-color;
$form-invalid-border-color:         $form-feedback-invalid-color;
$form-valid-color-dark:             $green-300;
$form-valid-border-color-dark:      $green-300;
$form-invalid-color-dark:           $red-300;
$form-invalid-border-color-dark:    $red-300;
Mais encore...

En savoir plus.