I would like to point out, that the IEmailService interface is part of the .net API, and not available in JavaScript.
So it’s only possible if you create implement it in .NET as a Dundas BI server extension, see the documentation here:
http://www.dundas.com/support/api-docs/net/#html/T_Dundas_BI_Services_IEmailService.htm%3FTocPath%3DLanguage%20Reference|Dundas.BI.Core%20Assembly|Dundas.BI.Services|IEmailService%20Interface|_____0
If you need to use JavaScript, you may use JavaScript to open the prefilled email message:
window.open(‘mailto:test@test.com?subject=subject&body=body’);
But it’s not automated, it will simply open up the email application with pre-filled information.
Please note, the email functionality isn’t exposed in REST or JS deliberately because it would allow any arbitrary users to send emails from the server, and this would be regarded as a security issue.