capture the date when state change
One answer
The JavaScript attribute customization does not provide any means to perform automation on state change. It is not possible to detect a state change and to do something based on it. You can only get the current work item information e.g. the state or attribute data.
I know some users have used tricks storing timestamps e.g. the last modified time to be able to detect a state change had happened and do something with that information. I am not necessarily a fan of those approaches.
Please check https://rsjazz.wordpress.com/2016/07/15/rtc-process-customization-what-you-can-and-cannot-do/ which is a summary of what I learned and what my best practice have been die to that.