logging duration with xAPI

Hi everyone, 

I'm trying to log duration with xAPI and encounter some problems.

The first problem is already solved - I had to find out how to get and store the elapsed time on a slide. 

This article was great help: http://iconlogic.blogs.com/weblog/2014/12/adobe-captivate-system-time-variables.html

My problem is now that I don't manage to send the ISO-converted time to xAPI and to retain it in my data,

which I'm downloading from scorm cloud via a get request with postman.

Here's my code, Im basically trying to get the elapsed time - which I calculated before using the proposed method from the iconlogic blog -

and to convert it to an iso string and to assign it to the result duration variable:

var tincan = new TinCan ({url: window.location.href});

 

var duration_conv = window.cpAPIInterface.getVariableValue("elapsed_time_slide1");

 

 

tincan.sendStatement(

{

    "verb": {

        "id": "http://adlnet.gov/expapi/verbs/completed",

        "display": {

            "en-US": "completed"

        }

    },

"object": {

        "id": "http://COSIMA_TP4_SIM_AINMUELLER/main_question_menu",

        "definition": {

            "name": {

                "en-US": "main_question_menu"

            },

         "description": {

                "en-US": "Menu for main questions"

            }

        },

        "objectType": "Activity"

    },

 

"result": {

    "duration": new Date(duration_conv).toISOString()

  }

}

 

);