add classname to all of a tag

[Tails]

Is it possible to add a className to specific tags on a page by their
index? I tried a loop like this and the property is not supported.

document.all("IMG")[0].className=="drag"

[cheesebagpipe]

var img, i = 0, allIMGs = document.getElementsByTagName('img');
while (img = allIMGs.item(i++)) img.className = 'drag';