// JavaScript Document
divs = ['d1','d2','d3','d4','d5','d6','d7'];

function hideDivs() {
for (var i=0; i<divs.length; i++)
document.getElementById(divs[i]).style.display = 'none';
}

function showDiv() {
hideDivs(); //hide them all before we show the next one.
var randomDiv = divs[Math.floor(Math.random()*divs.length)];
var div = document.getElementById(randomDiv).style.display =
'block';
}