JS owl progress bar

script.js

$(function () {
	// слайдер с прогрессом
	// 					  - [all]
	var owlPromo = $('.js-promo__items');
	var owlPromoTimer = 9000;
	var owlPromoSpeed = 1000;
	function promo_start (event) {
		var duration = owlPromoTimer;
		if(event == 'change') {
			duration -= owlPromoSpeed;
		}
		$('.promo__progress-val').css({
			width: '100%',
			'transition-duration': duration+'ms',
		});
	}
	function promo_reset () {
		$('.promo__progress-val').css({
			width: 0,
			'transition-duration': '0ms',
		});
	}
	owlPromo.owlCarousel({
		items: 1,
		loop: true,
		smartSpeed: owlPromoSpeed,
		slideBy: 1,
		nav: false,
		dots: false,
		autoplay: true,
		autoplayTimeout: owlPromoTimer,
		onInitialized: function () { promo_start('init'); },
		 onTranslated: function () { promo_start('change'); },
		  onTranslate: function () { promo_reset(); },
		       onDrag: function () { promo_reset(); },
		    onChanged: function (event) {
		    	if(event.item.index != null) {
		    		var obj = $(event.target).find('.owl-item');
		    		var nextPreview = obj.eq(event.item.index + 1).children('.promo__item').data('preview');
			    	$('.next__img').attr('src', nextPreview);

			    	var currentTitle = obj.eq(event.item.index).children('.promo__item').data('title');
			    	$('.next__title').text(currentTitle);
			    }
		    },
	});
});