Observe field is the most important part of brightscript language ;-
We can use observe field in several places like-

1 ) In any Interface field we can use observe field like when data come then callback function will run.
2 ) In any button when we click on that button then callback function will run .
3 ) In every xml element group, button and all we can use observe field.

In Roku development, the observeField function is used to monitor changes in the value of a field within a component's associative array. This is particularly useful in scenarios where you want to update the UI or perform certain actions based on changes to specific data.

Considerations:

  • Ensure that the field you're observing is part of the component's associative array (m in the example). If it's not, the observation won't work.
  • Be mindful of memory usage, especially when observing multiple fields or in components with frequent updates. Unregister observations when they're no longer needed to avoid memory leaks.

Observe Field take 2 parameter field first one is name or attributes on any xml element and interface element and seconds one is callback funciton if any changes occur in first part then callback function will fire automatically.

https://erpsolutions.oodles.io/developer-blogs/Observe-Field-in-roku/