Hi @rohit.mat!
Please see eazyBI documentation on how to create JavaScript calculated fields: JavaScript calculated custom fields.
You would define the field ID, name and data_type followed by the javascript_code in the eazyBI advanced settings:
[jira.customfield_nbux_workstreams]
name = "NBUX WorkStreams"
data_type = "text"
javascript_code = '''
// your code goes here
'''
Before defining the field, you can test the JS code in eazyBI Jira import options / Additional options as described.
See the following community post with an example of a custom dimension based on the Label field: Create dimension based on labels of jira tickets - #2 by janis.plume.
Lauma / support@eazybi.com