terriko

In the course of my thesis work, I made myself a little Firefox plugin that tells me where the javascript/dynamic parts are in a page. It's a fun little thing, just puts some big coloured boxes up, and I used it to help understand how people were using javascript in practice. It's one of those things I should probably release just 'cause it's fun, but I didn't have time to maintain in any meaningful way so I didn't get around to it.

Anyhow, I pulled it out last week to see what state it's in because I want to adapt some ideas from it, and it wasn't working. Which is odd, 'cause it's really quite simple. The core is just a loop that goes through each page element and looks for stuff like onmousover events:


var allTags = document.getElementsByTagName("*");
for each (var tag in allTags) {
  // ... do some stuff
}

And in debugging it, I've learned that getElementsByTagName("*"), which apparently used to return all the tags as objects, is now returning all the tags as well as, inexplicably, a number. It's not the same number for every page, and most of them seem to be around one thousandish on the simpler pages I was trying to test. Which sort of makes me think that maybe it's returning the number of tags, or that it sometimes returns an ordinal index for a single tag instead of an object, but why?

As it turns out, it didn't take much to get my add-on back up and running, just a quick check to see if the "tag" in question was in fact an object. But I'm left with a question: why has this changed in Firefox since I initially made the add-on? I'm not even sure where to ask, since it doesn't seem like it's a thing that changed in the specs. I'm recording it here for posterity so I remember to try to look it up later, but if you happen to know what's going on, please get in touch!