OK, I made a mistake. I know, my wife will be amazed that I admit that, but it does happen. Testing another developer's code, I missed a critical error. Consider the following bit of code:
cMessage += $.trim(StartDate).length == 0 ? "Start date is required.\n" : "";
cValue = $("#StartDate").val();
Do you see it? The conditional, in the ternary operator, should be looking at cValue, but what the developer had intended to rename that variable. There is no StartDate variable in the script, so it should error out as undefined.
And, in Internet Explorer, it does error. StartDate doesn't exist. But, I screwed up. I tested this code in Firefox, and it didn't throw an error, even though that value was empty. You know why? Well, if you put StartDate in the Firebug console, instead of undefined it gives you this:
Yes, that's right, because StartDate was an exact case match to the id of an element in the DOM, it returned the actual DOM element (which, by the way, is a valid string with a length).
Now, I'm not going to complain about who's right and who's wrong in this scenario (the value of StartDate), but it does underline the importance of testing in all browsers.