Make Reveal.js compatible with clickers that only have up/down buttons. See https://github.com/hakimel/reveal.js/issues/288

reveal-clicker-compatibility.js

/**
 * Treat up/down as page-up, page-down, so that clicker will step through each slide instead of only up/down slides
 */
document.addEventListener( 'keydown', function( event ) {
	switch ( event.keyCode ) {
		// k, up
		case 75:
		case 38:
			Reveal.navigatePrev();
			break;

		// j, down
		case 74:
		case 40:
			Reveal.navigateNext();
			break;
	}
} );