alert() is changing script function

I have a javascript function that works perfectly when I have an alert right before the final line, but when I take the alert out, it no longer works. How is this possible, and what can I do to fix it?
Here is what I have:

function setSelection(selectObject, value) {
for (var i = 0; i < selectObject.options.length; i++) {
if (selectObject.options[i].value == value)
{
alert(i);
selectObject.options[i].selected=true
}
}
}

If the alert is there, it selects the appropriate item. However, if I comment out the alert, the select box just selects the first item in the list. Any help is appreciated, as I am completely baffled.

Try using selectedIndex instead after the loop finishes. Once the correct element is found set selectedIndex to i and abort the loop.

Thanks for your reply! I tried that, but I get the same result: If the alert is not there, it selects the first item in the list, but if the alert is there, it selects the item I tell it to. One thing I did notice: It selects the first item in the list every time, but then after I click "OK" on the alert, it changes the selected item to the one I want it to be.

(In case that doesn't make sense, I'm converting a textbox to a select via ajax, so when the select appears, it selects the first item in the list. If I have the alert there, it then selects the correct item, but if it is not, it seems to just skip it. I had thought it might be a timing issue, but putting in code to make it wait doesn't really seem to work either, unless I am doing it wrong.)

Sounds like a race condition to me. The alert is changing the timing of the competing conditions.
[ April 30, 2007: Message edited by: Bear Bibeault ]

Any idea how I can fix it? I tried putting in something to make it wait for a bit, but it ended up delaying the whole switch from textbox to select, rather than waiting in the spot where I put the wait code. My js is pretty rough; any hints would be appreciated. Thanks!

What code is performing the switch? Why is the setting of the selection not part of that code? You need to be sure that the select element exist before trying to manipulate it.

Also you can simplify your selection set code to:

for single-selection select elements.

Here is the full set of code:

I tried using this js code I found:

and I put in a call to pausecomp in place of the alert, but that delayed everything for some reason, instead of just waiting a bit right before selecting the item.

In case you need it, here is the html that calls it:

[ April 30, 2007: Message edited by: K Dombroski ]

Please edit your repsonse using UBB code tags to preserve the formatting of the code. That's just too much code to look at in an unformatted block. Please read this for more information.

I went back and edited my previous post by adding the code tags. Thanks for the tip.

Ok, I think, after much experimentation, that this problem is actually an ajax issue. The list has not finished populating by the time I try to select an item in the list (due to the asynchronicity), so it doesn't go through the loop. I don't quite get why an alert works differently from a call to pausecomp, though. If I use the pausecomp method, everything waits (including displaying the dropdown instead of the text box, even though that code is called several lines earlier and does not use any ajax), but if I use the alert, the ajax call continues with no troubles, and by the time I hit "OK" the list is populated, so I can select something. How can I make it so that it does not try to select anything until after the list is loaded? I am using the DWR toolkit and am very new to ajax.

Your code that manipulates the select should be in the same thread that creates it, or at least triggered by that thread. That way, you know that the code won't execute until after the select element is in existence.

If you were using Prototype, you could use one of the onSuccess or onComplete callbacks to perform the selection after the Ajax request is complete. I'm sure that DWR must give you similar capabilities.

Thanks so much! Based on your suggestion, I looked up how I could do that with DWR, and came up with this, which is working like a charm:

Thanks again!

Too cool!

The lesson to be learned here is that, once you start adding Ajax into the picture, you can't assume that everything executes in a nice orderly and synchronous manner. You must be very cautious of introducing race conditions in which unrelated threads have inter-dependencies.