Filter widget select boxes based on a criteria.

filter-widget-selectboxes.js

// Edit this object with the id of the select element and a array of values to
// keep.
var optionsToKeep = {
  'activity-pcat256': [0, 1],
  'activity-pcat258': [0, 2, 3],
  'activity-pcat257': [0, 4, 5]
};

var filterSelectBoxes = function(options) {
  var toDelete = [];

  [].forEach.call(Object.keys(options), function(key) {
    // Fetch the element from the DOM tree
    var containers = document.querySelectorAll('.passenger-selector-container');

    [].forEach.call(containers, function(container) {
      var select = container.querySelector('#' + key);

      // Add the elements to a array that don't fit the conditions
      [].forEach.call(select.children, function(child) {
        if (options[key].indexOf(Number(child.value)) === -1) {
          toDelete.push(child);
        }
      });
    });
  });

  // Delete all the elements in the array from the DOM tree
  [].forEach.call(toDelete, function(option) {
    option.remove();
  });  
};

// When the page is done loading all of the content
document.addEventListener('DOMContentLoaded', function() {
  // Filter the select boxes according to the above options
  filterSelectBoxes(optionsToKeep);

  // create an observer instance
  var observer = new MutationObserver(function(mutations) {
    filterSelectBoxes(optionsToKeep);   
  });

  // configuration of the observer:
  var config = { subtree: true, childList: true };

  // pass in the target node, as well as the observer options
  observer.observe(document.querySelector('.passenger-selector-container'), config);
});