function updateControls()

in js/reveal.js [3468:3536]
45 lines of code
23 McCabe index (conditional complexity)

	function updateControls() {

		var routes = availableRoutes();
		var fragments = availableFragments();

		// Remove the 'enabled' class from all directions
		dom.controlsLeft.concat( dom.controlsRight )
						.concat( dom.controlsUp )
						.concat( dom.controlsDown )
						.concat( dom.controlsPrev )
						.concat( dom.controlsNext ).forEach( function( node ) {
			node.classList.remove( 'enabled' );
			node.classList.remove( 'fragmented' );

			// Set 'disabled' attribute on all directions
			node.setAttribute( 'disabled', 'disabled' );
		} );

		// Add the 'enabled' class to the available routes; remove 'disabled' attribute to enable buttons
		if( routes.left ) dom.controlsLeft.forEach( function( el ) { el.classList.add( 'enabled' ); el.removeAttribute( 'disabled' ); } );
		if( routes.right ) dom.controlsRight.forEach( function( el ) { el.classList.add( 'enabled' ); el.removeAttribute( 'disabled' ); } );
		if( routes.up ) dom.controlsUp.forEach( function( el ) { el.classList.add( 'enabled' ); el.removeAttribute( 'disabled' ); } );
		if( routes.down ) dom.controlsDown.forEach( function( el ) { el.classList.add( 'enabled' ); el.removeAttribute( 'disabled' ); } );

		// Prev/next buttons
		if( routes.left || routes.up ) dom.controlsPrev.forEach( function( el ) { el.classList.add( 'enabled' ); el.removeAttribute( 'disabled' ); } );
		if( routes.right || routes.down ) dom.controlsNext.forEach( function( el ) { el.classList.add( 'enabled' ); el.removeAttribute( 'disabled' ); } );

		// Highlight fragment directions
		if( currentSlide ) {

			// Always apply fragment decorator to prev/next buttons
			if( fragments.prev ) dom.controlsPrev.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); el.removeAttribute( 'disabled' ); } );
			if( fragments.next ) dom.controlsNext.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); el.removeAttribute( 'disabled' ); } );

			// Apply fragment decorators to directional buttons based on
			// what slide axis they are in
			if( isVerticalSlide( currentSlide ) ) {
				if( fragments.prev ) dom.controlsUp.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); el.removeAttribute( 'disabled' ); } );
				if( fragments.next ) dom.controlsDown.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); el.removeAttribute( 'disabled' ); } );
			}
			else {
				if( fragments.prev ) dom.controlsLeft.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); el.removeAttribute( 'disabled' ); } );
				if( fragments.next ) dom.controlsRight.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); el.removeAttribute( 'disabled' ); } );
			}

		}

		if( config.controlsTutorial ) {

			// Highlight control arrows with an animation to ensure
			// that the viewer knows how to navigate
			if( !hasNavigatedDown && routes.down ) {
				dom.controlsDownArrow.classList.add( 'highlight' );
			}
			else {
				dom.controlsDownArrow.classList.remove( 'highlight' );

				if( !hasNavigatedRight && routes.right && indexv === 0 ) {
					dom.controlsRightArrow.classList.add( 'highlight' );
				}
				else {
					dom.controlsRightArrow.classList.remove( 'highlight' );
				}
			}

		}

	}