Embedded HTML
Not JavaScript in the strictest sense, but this field is the best way to embed existing content or use HTML elements that are not supported by Antetype natively.
Example: Youtube Video
To embed a YouTube video, simply right-click on the video and select “copy embed code”:

and then paste into the HTML field:

Attention
Currently, mouse handling can cause problems during editing. If in doubt, use the popover/style inspector for styling. There is also no difference between edit mode and presentation mode.
Example: Use HTML
In HTML5, there are some interesting controls that you can use in a prototype. Here e.g. input type="range":

shows a nice functional slider that can be used with JavaScript, to intercept events etc.
Note
The general styling of HTML elements can be done via the header_incluide.html file.