So, if dont want to use conditional_fields module and only conditional fields core
You can do it, but required field have sometime a little bug.
In the issue someone take some code from conditional_fields that fix this issue, and use it.
your_module/js/conditional_fields.js
(function ($, Drupal) {
// Fix core's required handling.
$(document).bind('state:required', function (e) {
if (e.trigger) {
var fields = $(e.target).find('input, select, textarea, fieldset');
fields.each(function() {
var label = 'label' + (this.id ? '(for=' + this.id + ')' : '');
var $field_labels = $(e.target).find(label);
var $fieldset_legends = $(e.target).find('legend span.fieldset-legend');
var $labels = $field_labels.add($fieldset_legends);
if (e.value) {
$(this).attr({ required: 'required', 'aria-required': 'aria-required' });
$labels.each(function() {
$(this).addClass('js-form-required form-required');
});
} else {
$(this).removeAttr('required aria-required');
$labels.each(function() {
$(this).removeClass('js-form-required form-required');
});
}
})
}
});
})(jQuery, Drupal);
In your_module.module in a form alter add:
$form('#attached')('library')() = 'your_module/conditional_fields';
$form('field_b')('#states') = (
'visible' => (
':input(name="field_a")' => ('!value' => '_none')
),
'required' => (
':input(name="field_a")' => ('!value' => '_none'),
),
);
Don’t forget add the js code in your_module.libraries.yml file
Adding JS to a Drupal module
With our above code it worked!.
