jQuery validation plugin and Bootstrap 4

Solution:

https://jqueryvalidation.org/jQuery.validator.setDefaults/

jQuery.validator.setDefaults({
    errorElement: 'span',
    errorPlacement: function (error, element) {
        error.addClass('invalid-feedback');
        element.closest('.form-group').append(error);
    },
    highlight: function (element, errorClass, validClass) {
        $(element).addClass('is-invalid');
    },
    unhighlight: function (element, errorClass, validClass) {
        $(element).removeClass('is-invalid');
    }
});

The set defaults as discribed will work on bootstrap 4 with the following :

jQuery.validator.setDefaults({
    highlight: function(element) {
        jQuery(element).closest('.form-control').addClass('is-invalid');
    },
    unhighlight: function(element) {
        jQuery(element).closest('.form-control').removeClass('is-invalid');
    },
    errorElement: 'span',
    errorClass: 'label label-danger',
    errorPlacement: function(error, element) {
        if(element.parent('.input-group').length) {
            error.insertAfter(element.parent());
        } else {
            error.insertAfter(element);
        }
    }
});

dont forget to add the class class="form-control" to the input field. The only thing i was not able to find is how to get the input field colored red when it has an error or green when its ok. Maybe any can add that option to my answer ?

above an indicator solution didn't have the desired input spacing with the error label, use the code below and see the most pleasant result

jQuery.validator.setDefaults({
    onfocusout: function (e) {
        this.element(e);
    },
    onkeyup: false,

    highlight: function (element) {
        jQuery(element).closest('.form-control').addClass('is-invalid');
    },
    unhighlight: function (element) {
        jQuery(element).closest('.form-control').removeClass('is-invalid');
        jQuery(element).closest('.form-control').addClass('is-valid');
    },

    errorElement: 'div',
    errorClass: 'invalid-feedback',
    errorPlacement: function (error, element) {
        if (element.parent('.input-group-prepend').length) {
            $(element).siblings(".invalid-feedback").append(error);
            //error.insertAfter(element.parent());
        } else {
            error.insertAfter(element);
        }
    },
});