[assd18]

А если так:

var Data = function(type, opts){
			this.type = type;
			this.opts = opts;
		}
		
		var UserData = function(email, pass){
			this.email = email;
			this.pass = pass;
		}

		
		var ReqReg = function (){
			this.type = 'reg';
			this.opts = new UserData($("#regEmail").val(), $("#pass").val());
		
		}
		
		ReqReg.prototype = new Data();
		
		reqType = new ReqReg();

		var jsonText = JSON.stringify(reqType);
		alert(jsonText);