How do I get a custom comment field to pop-up based on another customer field value?

[tony randazzo]

I have a custom field called Cap, and currently you can select Yes or the default of None.  When the custom Cap field value = None, I would like a custom Comment field to appear to allow the user to enter a reason for the value.  Is this possible?  We are currently on the Jira Datacenter version, but are actively transitioning to the Atlassian Jira hosted Cloud version. 

BTW, I know this is possible if part of the workflow, but that is not the case here.

[Trudy Claspill]

Hello @tony randazzo 

Welcome to the Atlassian community.

Jira Cloud does not offer native functionality to display field A based on the value of field B. To do that you would need a third party app. Adaptavist has its Behaviours - ScriptRunner for Jira app that support that sort of functionality, but there are limitations. You should review their documentation to see if it would meet your needs.

https://marketplace.atlassian.com/apps/1228522/behaviours-scriptrunner-for-jira-cloud?hosting=cloud&tab=overview