Help pulling info from Reference Field on Record Producer

[Nic Omaha]

Hello, 

I have a record producer where the individual chooses an event to participate in on a reference field. Let's just say this field is "Event_Interested_In" which is mapped to the custom table "u_events". As they fill out the form I would like to write a on change client script for another field, lets say "phone" that it checks the event selected and if on that record "u_tshirts_provided" is "True" then a variable on the record producer is "u_tshirt_size" is changed to "true".  Everything I have tried hasn't worked since you can't dot walk on the ui policy. Not sure since this is a producer if maybe I should be using variables somewhere?

Here is where I kinda left off

function onChange(control) {
  // Since this is an onChange script, control will always be 'event_interested_in'
  var selectedRecord = g_form.getReferenceRecord('event_interested_in'); // Get selected record from 'event_interested_in'

  // Check if a record is selected and 'u_tshirts_provided' is true 
  if (selectedRecord && selectedRecord.u_t_shirts_provided == 'true') {
    g_form.setValue('shirts', 'true');
  } else {
    g_form.setValue('shirts', '');
  }
}

[Sandeep Rajput]

@Nic Omaha Please update your script as follows and check if it works for you.

function onChange(control, oldValue, newValue, isLoading, isTemplate) {
    if (isLoading || newValue === '') {
        return;
    }

    //Type appropriate comment here, and begin script below
    // Since this is an onChange script, control will always be 'event_interested_in'
    var selectedRecord = g_form.getReference('event_interested_in', eventCallback); // Get selected record from 'event_interested_in'

    function eventCallback(selectedRecord) {
        // Check if a record is selected and 'u_tshirts_provided' is true 
        if (selectedRecord && selectedRecord.u_t_shirts_provided == 'true') {
            g_form.setValue('shirts', 'true');
        } else {
            g_form.setValue('shirts', '');
        }
    }
}