xxxxxxxxxx1
<div class="container mt-5">2
<form class="needs-validation" novalidate>3
<div class="form-group">4
<select class="custom-select browser-default" required>5
<option value="">Open this select menu</option>6
<option value="1">One</option>7
<option value="2">Two</option>8
<option value="3">Three</option>9
</select>10
<div class="invalid-feedback">Please select one option</div>11
</div>12
<button class="btn btn-primary btn-sm" type="submit">Submit form</button>13
</form>14
</div>15
1
1
xxxxxxxxxx1
(function() {2
'use strict';3
window.addEventListener('load', function() {4
// Fetch all the forms we want to apply custom Bootstrap validation styles to5
var forms = document.getElementsByClassName('needs-validation');6
// Loop over them and prevent submission7
var validation = Array.prototype.filter.call(forms, function(form) {8
form.addEventListener('submit', function(event) {9
if (form.checkValidity() === false) {10
event.preventDefault();11
event.stopPropagation();12
}13
form.classList.add('was-validated');14
}, false);15
});16
}, false);17
})(); Console errors: 0