Tuesday, 16 March 2010

...by any other name, would smell as sweet

Although it's not a new problem, lately I've been seeing so many people running into a specific issue with Internet Explorer that I thought it worth just jotting down what the problem is and how to get around it.

The problem, in brief, is conflation. Internet Explorer (v6 and v7) mixes together the namespaces of the id and name attributes, which should be completely distinct from one another. id, you'll recall, must be unique within the document; it uniquely identifies an element. name, on the other hand, is not for uniquely identifying things (well, not mostly). It's used for a couple of different things, such as giving form fields the names they'll have when submitted, or giving anchors a name. There's no requirement that name values be unique — in fact, when doing forms, there are lots of reasons for using the same name for multiple fields (radio buttons, for example).

Unfortunately, the Internet Explorer engine will find elements by name sometimes when it really shouldn't, specifically when you're using document.getElementById. So for instance, say you have a form in your document with a 'stuff' field:

<input type='text' name='stuff'>
and later in that same document you have a div with the id "stuff":
<div id='stuff'>...</div>
Consider this code:
var elm;
elm = document.getElementById('stuff');
if (elm) {
alert("The element's tagName is " + elm.tagName);
else {
alert("Couldn't find the element.");
In a browser that implements document.getElementById correctly, that should alert "The element's tagName is DIV". But on IE, it will alert "The element's tagName is INPUT" because it incorrectly finds the input field. The only way around this is to change the id or name of one element or the other.

Another related problem is that id values are not case-sensitive in IE6 or IE7, although of course the standard says they should be. So it'll also confuse an element with the id (or name) 'stuff' with one with the id (or name) 'Stuff'. (To be fair, surely you and I would as well?)

There's good news, though: Microsoft does document the behavior, and they've fixed it in IE8, so there's hope for the future.

Perhaps slightly OT, but lest people accuse me of Microsoft-bashing (er, I have been known...), let me just remind everyone who brought us XMLHttpRequest (the basis of Ajax) and innerHTML, both of which I use (directly or indirectly) in nearly every JavaScript-enabled browser project I do — and I bet you do too. So hey, they got many things wrong, but got some things very right as well. Also useful to remember — as we continue to bash IE6 with repeated shouts of "Die! Die!" — just how much amazingly better (faster, less crash-prone, more feature-rich) it was than its chief rival, back in the day.


Robert Bram said...

Thanks for this - what an awful hole left wide open.. ID itself is broken in these browsers.

T.J. Crowder said...

So I just learned something new: jQuery has been quietly working around this problem for people for more than four years. Talk about how a good library can save you time and trouble...