How can I call javascript from another site?
You could add the JS in code.

e.g:

/**
 * Implements hook_init
 */
function mymodule_init(){
  if ($node = menu_get_object('node')) {
    if ($node-&gt;type == 'my_type') {
      $items = field_get_items('node', $node, 'field_my_nid_field');
      if (!empty($items[0]['value'])) {
        $nid = filter_xss($items[0]['value']);
        drupal_add_js('
        widgetContext = { "url": "http://theirsite.com/mysite/'.(int)$nid.'", "width": "600", "height": 200, "widgetid": "web_widget_iframe_hash" };
        ', array('type' =&gt; 'inline', 'scope' =&gt; 'header'));
      }
    }
  }
}


The other static script tag can be added in a custom Full HTML block / content pane or similar, where you want the content to display.