onScroll(evt) {
            this.scrollTop = evt.target.scrollTop;
            this.firstItemToRender = Math.floor(this.scrollTop / this.itemHeight);
            this.lastItemToRender = this.firstItemToRender + Math.ceil(this.$el.clientHeight / this.itemHeight);
        }
/**
         * @param evt - the scroll event
         */
@param evt - the scroll event
@param evt - the scroll event
onScroll(evt) {
            this.scrollTop = evt.target.scrollTop;
            this.firstItemToRender = Math.floor(this.scrollTop / this.itemHeight);
            this.lastItemToRender = this.firstItemToRender + Math.ceil(this.$el.clientHeight / this.itemHeight);
        }
onScroll ( evt ) { this . scrollTop = evt . target . scrollTop ; this . firstItemToRender = Math . floor ( this . scrollTop / this . itemHeight ) ; this . lastItemToRender = this . firstItemToRender + Math . ceil ( this . $el . clientHeight / this . itemHeight ) ; }
@param evt - the scroll event
@param evt - the scroll event