The JS editor manual describes Cyclic, Change, Scheduled, Once, Aligned Cycle, Function Block, Rising Edge, Falling Edge and Value Change Callback modes. Cyclic executes at the configured interval; Change executes when any selected tag changes; Once runs at gateway startup; Scheduled runs at the specified time.
Rising Edge means 0→1 and Falling Edge means 1→0. Function Block provides a subprogram for other scripts. A value-change callback receives the tag name, current value and quality. The 1000 ms cyclic setting in the manual is an example, not a universal minimum cycle or script-count limit.