Set backstretch image of page from image content type in drupal, and change css on scroll down

script.js

  function commercial_backstretch_setup() {
    if($('.node-type-commercial-development').length > 0) {
      var image = $('#content .field-image img').attr('src');
      $('body').backstretch(image);

      var height = $(window).scrollTop() - $('#testimonial_wrapper').offset().top
      if(height > $('#content').height()) {
        $('#content').height(height * -1);
      }
    }
  }

First if statement was used to prevent it from happening on a specific page