The timing of a web page running an experiment looks something like this:
1- Your HTML starts loading
2- Optimizely's code starts loading (typically with a version of jQuery included)
When the experiments run, they usually run while #3 is still happening, so more often than not, those functions and plugins will not be available to use when the variation's code executes.
You can force Optimizely to wait until after your version of jQuery (and it's plugins) are loaded by using
Whenever you prefix a comman with "window." it forces Optimizely to look for the window-scoped function rather than the Optimizely scoped version. This is very useful when you have a bunch of code that works in your console but doesn't work when you run it inside of an experiment.