ninja-forms-three-custom-field-validation-5.js

// Create a new object for custom validation of a custom field.
var myCustomFieldController = Marionette.Object.extend( {
    initialize: function() {

        // On the Form Submission's field validaiton...
        var submitChannel = Backbone.Radio.channel( 'submit' );
        this.listenTo( submitChannel, 'validate:field', this.validateRequired );

        // on the Field's model value change...
        var fieldsChannel = Backbone.Radio.channel( 'fields' );
        this.listenTo( fieldsChannel, 'change:modelValue', this.validateRequired );
    },

    validateRequired: function( model ) {

        // Only validate a specific fields type.
        if( 'custom' != model.get( 'type' ) ) return;

        // Only validate if the field is marked as required?
        if( 0 == model.get( 'required' ) ) return;

        // Check if Model has a value
        if( model.get( 'value' ) ) {
            // Remove Error from Model
            Backbone.Radio.channel( 'fields' ).request( 'remove:error', model.get( 'id' ), 'custom-field-error' );
        } else {
            // Add Error to Model
            Backbone.Radio.channel( 'fields' ).request( 'add:error', model.get( 'id' ), 'custom-field-error', 'This is an error message' );
        }
    }
});

// On Document Ready...
jQuery( document ).ready( function( $ ) {

    // Instantiate our custom field's controller, defined above.
    new myCustomFieldController();
});

My question is... where do I have to put this code in the ninja-forms plugin??

This code is not working and is giving error. Can you please provide proper instruction how to do this