onRender jquery plugin

onRender.js

// ---------------------------------------------------------------------------
// :: execute callback function when shiny output element is modified
// :: the callback can be called multiple times if you use option onTime: false
// :: you can also use check option with function that will be check if
// :: before executing callback and removing observer
// ---------------------------------------------------------------------------
$.fn.onRender = function(callback, options) {
  if (this.length === 0) {
    throw new Error("Element doesn't exists! Try to wait until it's added to DOM.");
  }
  var cancel = arguments[0] == 'cancel';
  if (cancel) {
    if (arguments.length === 3) {
      callback = arguments[1];
      options = arguments[2];
    } else if (arguments.length === 2) {
      options = arguments[1];
    }
  }
  var settings = $.extend({
    // if set to true will remove mutation observer after first mutation
    oneTime: true,
    // if set to true will always execute and clear mutation observer on first mutation
    // default will not fire callback when mution is recalcuation of any element
    strict: false,
    name: 'default',
    observer: {childList: true, subtree: true, attributes: true},
    check: function(node) { return node.closest('body').length; }
  }, options || {});
  var name = 'on-render-' + settings.name;
  if (cancel) {
    return this.each(function() {
      var self = $(this);
      var render = self.data(name);
      if (render) {
        var filter;
        if (typeof callback === 'function') {
          filter = render.specs.filter(function(spec) {
            return spec.callback !== callback;
          });
        } else {
          filter = render.specs.filter(function(spec) {
            return spec.name !== settings.name;
          });
        }
        render.specs = filter;
        if (render.specs.length === 0) {
          render.observer.disconnect();
          self.removeData(name);
        }
      }
    });
  } else {
    return this.each(function() {
      var node = $(this);
      var render = node.data(name);
      if (!render) {
        render = {
          specs: [],
          name: settings.name,
          observer: new MutationObserver(function(mutations) {
            mutations = mutations.filter(function(mutation) {
              return mutation.type == 'attributes' &&
                     mutation.attributeName == 'class' ||
                     mutation.type != 'attributes';
            });
            if (mutations.length) {
              render.specs.forEach(function(spec) {
                var settings = spec.settings;
                var callback = spec.callback;
                // if recalculating wait for next mutation
                if (!(node.hasClass('recalculating') ||
                      node.find('.recalculating').length) ||
                    settings.strict) {
                      if (settings.check(node)) {
                        callback.call(node[0]);
                        if (settings.oneTime) {
                          node.onRender('cancel', callback, settings);
                        }
                      }
                }
              });
            }
          })
        };
        render.observer.observe(node[0], settings.observer);
        node.data(name, render);
      }
      render.specs.push({
        settings: settings,
        name: settings.name,
        callback: callback
      });
    });
  }
};