the following MSDN article describes how to use the Client PeoplePicker with Javascript:
http://msdn.microsoft.com/de-de/library/office/jj713593(v=office.15).aspx
I have an SharePoint hosted app (2013) and I am saving the user Keys to a hidden list in my app.
But what is the most elegant way to initialize the people picker with the previous saved users?
Btw: I am assuming that I already have a string Array with the correct user ids.