How to inject java code for JIRA custom field?

[Gayathri Bhukya]

Please some one can help me  with simple any java script example code.

Like writing some java script for custom field and save it as separately ex. test.js and call/load into JIRA for custom field action to perform.

[Yagnesh Bhat]

Custom fields are generally created thru plugins : https://developer.atlassian.com/jiradev/jira-platform/guides/fields/tutorial-creating-a-custom-field-type

[Steven F Behnke]

Developers usually package them up into add-ons – 

https://developer.atlassian.com/jiradev/jira-platform/building-jira-add-ons/jira-plugins2-overview/jira-plugin-module-types/web-resource-plugin-module

[Boris Georgiev _Appfire_]

It would be better if you give more details on what exactly you're trying to achieve i.e. what should this custom field do ?

There are a lot of ways to have "scripted field" which uses code to calculate values or do something else and most of the "non-hacky" approaches is to use a plugin like JJupin or Script Runner.

https://marketplace.atlassian.com/plugins/com.keplerrominfo.jira.plugins.jjupin/server/overview

https://confluence.kepler-rominfo.com/display/JJUP30/How+%27Live+Fields%27+work

https://scriptrunner.adaptavist.com/latest/jira/quickstart.html

https://scriptrunner.adaptavist.com/latest/jira/behaviours-overview.html

Also there is an "unsupported" option to inject JS code for custom fields

https://confluence.atlassian.com/jira/fields-allowing-custom-html-or-javascript-224401453.html