SP.Principal.id property (sp.js)
Gets a value that specifies the member identifier for the user or group.
Applies to: apps for SharePoint | SharePoint Foundation 2013 | SharePoint Server 2013
var value = SP.Principal.get_id ()
Return value
Type: Number
Remarks
Its value must be equal to or greater than 1. Its value must be equal to or less than 2147483647.