wp/app/themes/twentysixteen/js/keyboard-image-navigation.js

/**
 * Twenty Sixteen keyboard support for image navigation.
 */

( function( $ ) {
	$( document ).on( 'keydown.twentysixteen', function( e ) {
		var url = '';

		// Left arrow key code.
		if ( 37 === e.which ) {
			url = $( '.nav-previous a' ).attr( 'href' );

		// Right arrow key code.
		} else if ( 39 === e.which ) {
			url = $( '.nav-next a' ).attr( 'href' );

		// Other key code.
		} else {
			return;
		}

		if ( '' !== url && ! $( 'textarea, input' ).is( ':focus' ) ) {
			window.location = url;
		}
	} );
} )( jQuery );