function updateSlides()

in js/reveal.js [1593:1709]
94 lines of code
22 McCabe index (conditional complexity)

	function updateSlides( selector, index ) {

		// Select all slides and convert the NodeList result to
		// an array
		let slides = Util.queryAll( dom.wrapper, selector ),
			slidesLength = slides.length;

		let printMode = print.isPrintingPDF();
		let loopedForwards = false;
		let loopedBackwards = false;

		if( slidesLength ) {

			// Should the index loop?
			if( config.loop ) {
				if( index >= slidesLength ) loopedForwards = true;

				index %= slidesLength;

				if( index < 0 ) {
					index = slidesLength + index;
					loopedBackwards = true;
				}
			}

			// Enforce max and minimum index bounds
			index = Math.max( Math.min( index, slidesLength - 1 ), 0 );

			for( let i = 0; i < slidesLength; i++ ) {
				let element = slides[i];

				let reverse = config.rtl && !isVerticalSlide( element );

				// Avoid .remove() with multiple args for IE11 support
				element.classList.remove( 'past' );
				element.classList.remove( 'present' );
				element.classList.remove( 'future' );

				// http://www.w3.org/html/wg/drafts/html/master/editing.html#the-hidden-attribute
				element.setAttribute( 'hidden', '' );
				element.setAttribute( 'aria-hidden', 'true' );

				// If this element contains vertical slides
				if( element.querySelector( 'section' ) ) {
					element.classList.add( 'stack' );
				}

				// If we're printing static slides, all slides are "present"
				if( printMode ) {
					element.classList.add( 'present' );
					continue;
				}

				if( i < index ) {
					// Any element previous to index is given the 'past' class
					element.classList.add( reverse ? 'future' : 'past' );

					if( config.fragments ) {
						// Show all fragments in prior slides
						showFragmentsIn( element );
					}
				}
				else if( i > index ) {
					// Any element subsequent to index is given the 'future' class
					element.classList.add( reverse ? 'past' : 'future' );

					if( config.fragments ) {
						// Hide all fragments in future slides
						hideFragmentsIn( element );
					}
				}
				// Update the visibility of fragments when a presentation loops
				// in either direction
				else if( i === index && config.fragments ) {
					if( loopedForwards ) {
						hideFragmentsIn( element );
					}
					else if( loopedBackwards ) {
						showFragmentsIn( element );
					}
				}
			}

			let slide = slides[index];
			let wasPresent = slide.classList.contains( 'present' );

			// Mark the current slide as present
			slide.classList.add( 'present' );
			slide.removeAttribute( 'hidden' );
			slide.removeAttribute( 'aria-hidden' );

			if( !wasPresent ) {
				// Dispatch an event indicating the slide is now visible
				dispatchEvent({
					target: slide,
					type: 'visible',
					bubbles: false
				});
			}

			// If this slide has a state associated with it, add it
			// onto the current state of the deck
			let slideState = slide.getAttribute( 'data-state' );
			if( slideState ) {
				state = state.concat( slideState.split( ' ' ) );
			}

		}
		else {
			// Since there are no slides we can't be anywhere beyond the
			// zeroth index
			index = 0;
		}

		return index;

	}