Remove undefined from a Javascript object

I’ve been doing a fair amount of javascript programming lately, and I found myself needing to remove a nested object from an object.  Doing this is easy enough with the “delete” command, but it leaves you with annoying “undefined”s all over.  To get around that, I scoured the internet for a way to remove them easily.  Turns out that if efficiency isn’t a problem, it’s easier to drop the right objects into an array and then re-assign it.

var tmpArray = new Array();
for(el in {
     if([el]) {
} = tmpArray;

Easy and pie.