Access a PHP variable in JavaScript

Also see how to add via #attached property

Set variable in PHP:

drupal_add_js(array('my_module' => array('inactive_terms' => $testvar)), array('type' => 'setting'));

You need make proper checks for variable existence as this may break all existing JavaScript execution:

 Drupal.behaviors.example_behavior = {
    attach: function(context, settings) {

      // Check if the variable exist.
      var dSettings = Drupal.settings;
      if (dSettings.my_module != undefined) {         
        x = (dSettings.my_module.inactive_terms != undefined) ? dSettings.my_module.inactive_terms : ''; 
        if (x != '') {  
        // Variable exist.   
        }
      }

    }
  }