Chnage WordPress Posts by Arrow Keys

document.onkeydown = function (e) {
    var e = e || event,
    keycode = e.which || e.keyCode; 
    if (keycode == 37 || keycode == 33)	
	//FOR POST 
        location = "<?php echo get_previous_posts_page_link(); ?>";
	//FOR PAGES AS WELL
	location = "<?php echo get_permalink(get_adjacent_post()); ?>";
    if (keycode == 39 || keycode == 34)	
	//FOR POST 
        location = "<?php echo get_next_posts_page_link(); ?>";
	//FOR PAGES AS WELL
	 location = "<?php echo get_permalink(get_adjacent_post()); ?>";
}