Ironic
Ironically I have just been hit by exactly the same JavaScript error.
- uninstalled eCart
- wait 55 mins (thank you Adobe for making the extension manager so swift)
- tried again - all OK
Moral of this tale for me is not to install eCart. I never use it (it came bundled) and I only install it because I own it. All I ever seem to do with it is uninstall/install when I have issues with WA product/code versions. And as we all know, that takes an age ...