Change page to a picture after 5 seconds if it's Halloween

halloween.js

docucument.onload = function)() {
  var seconds = 5
	var today = new Date()
	if (today.getMonth() == 9 && today.getDate() == 31){
		setInterval(function(){
			body = getElementsByTagName('body');
			body[0].innerHTML = '<img src="http://i.imgur.com/iPOS6.gif">';
		}, (seconds*1000));
	}
}