Hi Jishnu,
To elaborate on Akshay's response:
You can build out a Web Template using liquid to retrieve the record from the Dataverse. You can modify the return type to be JSON, set on the field in the Web Template at the bottom of the form. You will need to accept some sort of parameter to filter the specific record you want to retrieve.
Once that is built, you can then build out a web page that has the page template attached to the web template. This will allow you to give it a specific URL to call from your JS code.
When the web page is built, you can use an AJAX or HTTP request to call your liquid service at that specified URL, pass it the parameter (probably the GUID of the record you want) and it will bring it back in JSON format.
Colin Vermander has an excellent blog about this approach: https://colinvermander.wordpress.com/2017/04/17/dynamics-365-portals-use-liquid-to-return-json-or-xml/
Alternatively, with the more recent versions of the Powerapps Portals, we now have the ability to utilize Portals Web APIs. There are some limitations and requirements around this, however, it allows us to use CRUD operations directly from JS. You can find out about this here: https://docs.microsoft.com/en-us/powerapps/maker/portals/web-api-overview
If you have any questions please let me know! I'd appreciate if you would mark this as answered if I was able to solve your issue!
Thanks!
Matt Bayes
