Well its difficult to show you how you could do it, without actually doing it for you. I would do it something like this, although i would use an array of phrases from each of the 12 days of the song. And i would calculate the length of it rather than hand coding etc..
Basically, if you created a for() loop, ( as you want it repetitive ),obviously you have 12 days of Christmas, so you want to repeat it 12 times. Each day, 1 - 2 - 3 - 4 - 5 - 6 ... etc.. You would have a switch statement do detect the day and add the appropriate phrase, like this:
Code:
var curday = 12;
var song = '';
for( curday = 2; curday > 0; curday-- ){
switch( curday ){
case 1:
song += 'A partridge in a pear tree' + '<br/>';
break;
case 2:
song += 'Two Turtle Doves' + '<br/>';
break;
}
}
document.write( song );