JS9 can perform local and remote tasks in response to region changes:

• choose a task by clicking one of the analysis buttons above
  • the region tasks are local (browser-based) tasks
  • spectrum, counts are remote tasks (requiring the back-end helper to be running)
• display an image by clicking on one of the data files
• create a region using the JS9 Region menu
• as you move/resize the region, the task will run on that region
• you can suspend task execution by unselecting xeqOnChange in the JS9 Region menu

See the page source for implementation details.