SetFocusOnChosenJsFieldWhenUsingJqueryUnobtrusiveValidation

// Add this to a Js file that loads after jquery.validate.js.
// Override the 'focusInvalid' function from jquery.validate.js to a custom function which includes setting the focus for chosen dropdowns
$.validator.prototype.focusInvalid = function () {
    if (this.settings.focusInvalid) {
        try {
            $(this.findLastActive() || this.errorList.length && this.errorList[0].element || [])
            .filter(":visible")
            .focus()
            // manually trigger focusin event; without it, focusin handler isn't called, findLastActive won't have anything to find
            .trigger("focusin");

            // CUSTOM BIT - trigger focus on the first chosenJs select list in error
            if (this.errorList.length) {
                if ($(this.errorList[0].element).hasClass("chosen-select")) {
                    $(this.errorList[0].element).trigger('chosen:activate');
                }
            }
        } catch (e) {
            // ignore IE throwing errors when focusing hidden elements
        }
    }
}

When using Chosen.js (https://harvesthq.github.io/chosen/) with Jquery UnobtrusiveValidation (typically with .NET MVC) - the focus wont be set to the first field in error if this is a Chosen Dropdown.
Override the jquery.validate.js function: 'focusInvalid' to add an additional check for this scenario.