Conditional module configuration fields?

[namhost]

I am creating a module and I want the flow for the configuration to be as follows:

1. The first line item must be:
   [ ] Enable API
2. Only if this checkbox is clicked, must the next field appear:
    API Key: ______________________________________

Is there an inherent way to do this? Or will I need to use javascript to show and hide the fields as needed? And if so, how do you add javascript to the admin backend? Is that possible?