Detect when hubspot form is submitted successfully

index.js

hbspt.forms.create({
  portalId: '', //Your portal ID
  formId: '', // Your form ID
  css: '',
  onFormReady: function(form, ctx) {
    form.parents('.hbspt-form:first').on('DOMSubtreeModified', function() {
      var hsForm = $(this);
      if(hsForm.find('.submitted-message').length) {
        //Your code.   
      }
    });
  }
});