How to get theme image path in javascript?

Inside template.php:

drupal_add_css(array('path_to_images' => base_path() . path_to_theme() .'/images'), 'setting');

Then from your script "Drupal.settings.path_to_images" will point to the right path.

$(".myclass").css(background:'url(' + Drupal.settings.path_to_images + '/myimage.png')');