in js/reveal.js [3889:3924]
function availableRoutes() {
var horizontalSlides = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ),
verticalSlides = dom.wrapper.querySelectorAll( VERTICAL_SLIDES_SELECTOR );
var routes = {
left: indexh > 0,
right: indexh < horizontalSlides.length - 1,
up: indexv > 0,
down: indexv < verticalSlides.length - 1
};
// Looped presentations can always be navigated as long as
// there are slides available
if( config.loop ) {
if( horizontalSlides.length > 1 ) {
routes.left = true;
routes.right = true;
}
if( verticalSlides.length > 1 ) {
routes.up = true;
routes.down = true;
}
}
// Reverse horizontal controls for rtl
if( config.rtl ) {
var left = routes.left;
routes.left = routes.right;
routes.right = left;
}
return routes;
}