JavaScript API for WordPress NinjaForms before submission

I am using WordPress Ninja Forms and I am trying to create a preview of a form to be accepted before submitting data via Ajax. This means I need to add custom JS code between the form validation and the submit process.

So far I have tried the following:

var form_id = 1;
var PreviewFormController = Marionette.Object.extend({

  initialize: function() {
    Backbone.Radio.channel( 'form-' + form_id ).reply( 'maybe:submit', this.PreviewForm, this, form_id);
  },

  PreviewForm: function(formID){

    var formModel = nfRadio.channel( 'app' ).request( 'get:form', formID );

    if(formModel.getExtra('previewOk')){
      return true;
    }
    this.ShowPreview( formModel );
    return false;
  },

  ShowPreview: function(formModel){
    if(confirm("You sure?")){
      nfRadio.channel( 'form-' + form_id).request( 'add:extra', 'previewOk', true );
      nfRadio.channel( 'form-' + formModel.get( 'id' ) ).request( 'submit', formModel );
    }
  }
});

$(function(){
    new PreviewFormController();
});

      

        
        
        
      

    

The problem is that PreviewForm

now comes before field validation. How can you connect the function after checking the field?

I am a bit lost as the Codex is not ready yet. I would be so glad if someone could help me.