f-etag/lib/index.js

a thin wrapper around fetch api to provide a basic level in memory cache for etags

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});
var data = {};
var etags = {};

exports.default = function () {
  var url = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : null;
  var options = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : { headers: {} };

  /* eslint no-param-reassign:0 */
  url = url ? url : options.url;
  if (options.method === 'GET' || !options.method) {
    var etag = etags[url];
    var cachedResponse = data['' + url + etag]; // ensure etag is for url
    if (etag) {
      options.headers['If-None-Match'] = etag;
    }

    return fetch(url, options).then(function (response) {
      if (response.status === 304) {
        return cachedResponse.clone();
      }

      if (response.status === 200) {
        var responseEtag = response.headers.get('Etag');

        if (responseEtag) {
          data['' + url + responseEtag] = response.clone();
          etags[url] = responseEtag;
        }
      }

      return response;
    });
  }
  // all other requests go straight to fetch
  // can't use apply(undefined, arguments) as babel uses _arguments which is different..
  return fetch.call(undefined, url, options);
};