Hi,
You need to write custom code in .NET using SharePoint DOM fetch the data and you ca use thew data in JavaScript.
You can achieve this by creating your .NETfunctionality in aspx page and calling the aspx page using dojo.xhrget (or) dojo.xhrpost. And in the call back handler of the dojo function you can get the data from the aspx page, which you can use in your JS API.
Let me know if you need more details.
Regards,
Ravi.