A Javascript terminal is a text window where you can execute Javascript scripts line-by-line or by blocks.

To make a new Javascript terminal window, select File ▸ New ▸ New Javascript window ⌘N.

In a Javascript terminal, ⌘R compiles and executes the current selection (or the current line if the selection is empty), and displays the result in the Console-Javascript window by default.
The menu Action lets you excecute, check the syntax or validate.

This behavior is the key to developing scripts in Smile, since it is how you debug a script piece by piece and how you test each line just written.

For more details about scripting, please consult Using Javascript in Smile.