yiiActiveForm ajax validation duplicate error messages in summary

[yuniorsk]

Right now there is inconsistency between server-side and client-side version of displaying error summary as server-side version shows only unique error messages and client-side shows all of them. As far as I can tell there's also no way to alter that behavior on client-side as summary rendering is done after the afterValidate event was triggered.

What steps will reproduce the problem?

ActiveForm with AJAX validation with multiple validation errors with same message (e.g. "Field is required").

What is the expected result?

Display only unique error messages and skip duplicates.

What do you get instead?

All error messages no matter if they is a duplicate or not.

[vadgus]

If someone uses old yii2 versions and cannot upgrade by some reasons:

$this->registerJs(<<<JS

$('div.error-summary ul').on('DOMSubtreeModified', function () {
    let uniqueErrors = {};
    $(this).find('li').each(function () {
        let thisVal = $(this).text();
        if (thisVal in uniqueErrors) {
            $(this).remove();
        } else {
            uniqueErrors[thisVal] = true;
        }
    })
});

JS
);