Random img con target diversi

[pariri]

Non funziona!
Ho fatto cosi:

var openInNewWin = false;

var banners = new Array();
banners[0] = new Banner("http://www.miosito.org/index.php", "title01", "img01.gif","<target= '_self'>");
banners[1] = new Banner("http://www.miosito.org/siamo.php", "title02", "img02.gif","<target= '_self'>");
banners[2] = new Banner("http://www.miosito.org/indirizzo.php", "title03", "img03.gif","<target= '_blank'>");


function Banner(url, description, image,target) {
this.url = url;
this.description = description;
this.image = image;
this.target = target;
return this;
}
var bNum = Math.round(Math.random() * (banners.length - 1));


document.write("<a href=\"" + banners[bNum].url + "\"");
if (openInNewWin) {
document.write(" target=\"" + banners[bNum].target + "\"");
}
document.write(">");
document.write("<img src=\"" + banners[bNum].image + "\" border=\"0\" alt=\"" + banners[bNum].description + "\">");
document.write("</a>");