Collection+JSON in-memory caching

collection_json_cache.js

const Cache = function(deps) {
  const self = {};
  const requested = {};

  self.fetch = function(href) {
    requested[href] = requested[href] || new Promise((resolve, reject) => {
      const collection = deps.Collection();
      collection.fetch(href).done(() => {
        resolve(collection);
      });
    });
    return requested[href];
  };

  return self;
};