Split Data for certain condition In JavaScript Pentaho

I have a column in csv file named event_name and I am using Modified Java Script Value step to create new columns if the first character of event_name fufill conditions , for example :

event_name ="app_connection: connection_start_time = 10/05/2018 17:29:26: connection_end_time = 10/05/2018 17:29:29: connection_duration_in_seconds = 3"

           ==> event = app_connection
           ==> connection_start_time = 10/05/2018 17:29:26
           ==> connection_end_time = 10/05/2018 17:29:29
           ==> connection_duration_in_seconds = 3

if it's : event_name ="scene_access"

==> event = scene_access

I tried this code but it doesn't seem to change anything :

            if(event_name.substr(0,3).equals("app"))
             {
               var event = event_name.substring(0,14);
               var connection_start_time = event_name.substr(40,59);
               var connection_end_time = event_name.substr(83,102);
               var connection_duration_in_seconds = event_name.substr(137,139);
               }
               else
                {
                  event_name = event_name;
                 }

If you could give me a hint or explaining what I'm missing will be a huge help. Thank you.