foo = new Ground.Collection('test');

  foo = new Ground.Collection('test');
  foo.observeSource(bar.find());
  Meteor.setTimeout(() => {
    // Stop observing - keeping all documents as is
    foo.stopObserver();
  }, 1000);

  foo.keep(bar.find());

  foo.keep(bar.find({}, { limit: 30 }));

  foo.keep(bar.find({ type: 'a' }, { limit: 30 }), bar.find({ type: 'b' }, { limit: 30 }));

  foo.clear();

GroundLegacy = {
  Collection: class GroundLegacy extends Ground.Collection {
    constructor(collection, options) {
      if (!(collection instanceof Mongo.Collection)) {
        throw new Error('GroundLegacy requires a Mongo.Collection');
      }
      if (options.cleanupLocalData !== false) {
        throw new Error('GroundLegacy requires cleanupLocalData to be false');
      }
      // Create an instance of ground db
      super(collection._name);
      this.mongoCollection = collection;
      collection.grounddb = this;
      // Observe on the whole collection
      this.observeSource(collection.find());
      // Store super
      collection.orgFind = collection.find;
      collection.orgFindOne = collection.findOne;
      // Overwrite collection finds using the grounded data
      collection.find = (...args) => {
        return this.find(...args);
      };
      collection.findOne = (...args) => {
        return this.findOne(...args);
      };
    }
    removeLocalOnly() {
      // Remove all documents not in current subscription
      this.keep(this.mongoCollection.orgFind());
    }
  },
};