I would like to make a field mandatory based on the value selection another field.at a state

https://jazz.net/wiki/bin/view/Main/AttributeCustomization explains the JavaScript (and Java) API and what conditions can access. Conditions can access the workflow action selected as well as the state of a work item. https://rsjazz.wordpress.com/2015/08/07/a-custom-condition-to-make-attributes-required-or-read-only-by-role-version-2/ explains how the UI works with condition and preconditions/operation advisors. Advisors basically prevent saving but don't provide UI hints. Conditions can provide UI hints.

https://jazz.net/library/article/495 is pretty outdated. Start here: https://rsjazz.wordpress.com/2015/09/30/learning-to-fly-getting-started-with-the-rtc-java-apis/

well, condition returns true or false. you cannot pass it parameters.. so you have to hard code the test..

once you have condition working, then you can use the condition in the required by condition advisor settings

you have to add the required by condition advisor to the list of active advisors..