How to get the list of Roles for particular Team area and then the list of users with a particular role using java script in RTC

No, it is not possible to access that data with JavaScript in an attribute customization.
You can only do this in Java based providers. See https://rsjazz.wordpress.com/2013/06/26/attribute-customization-java-based-value-providers-conditions-and-validators/

Thanks  a  lot , Ralph!

Hello  Ralph . 
I  have  some another  issue  . 
I  should to  calculate  the  Owner field .
I  have developed  the  calculated  value  that  returns Creator  as  icontributor .
I  can  see my Calculated Value on  field  definition  on  drop  down of  Calculate value  for  attributes that have  been  defined as  contributors . 
I   define  the  dependency from  Filed Against  attribute . 
When  I  set my Calculated  value  to  custom contributor attribute  it  gets  the name  of  creator  by  the  moment  the   Filed Against  attribute has  been  changed ,  but after  the  save process  the  value  of  the custom  contributor  attribute  becomes to  be  Unidentified . 
If  I set my Calculated  value  to Owned By  attribute  with the same dependency  it  also  gets  the right  value  before  saving  , but  on  save  process  I  get  the next error :  "Error running operation 'Saving Work Item'

java.lang.NullPointerException
java.lang.NullPointerException"

Please  advice .