How to use the pouchdb-fetch.Headers function in pouchdb-fetch

var ourFetch = function (url, options) {

    options = options || {};
    options.headers = options.headers || new Headers();

    options.credentials = 'include';

    if (opts.auth || host.auth) {
      var nAuth = opts.auth || host.auth;
      var str = nAuth.username + ':' + nAuth.password;
      var token = btoa(unescape(encodeURIComponent(str)));
      options.headers.set('Authorization', 'Basic ' + token);
    }

    var headers = opts.headers || {};
    Object.keys(headers).forEach(function (key) {
      options.headers.append(key, headers[key]);
    });

    /* istanbul ignore if */

return result;
      }).then(postprocessAttachments(opts));
    }

    // We are using a temporary view, terrible for performance, good for testing
    body = body || {};
    Object.keys(fun).forEach(function (key) {
      if (Array.isArray(fun[key])) {
        body[key] = fun[key];
      } else {
        body[key] = fun[key].toString();
      }
    });

    return db.fetch('_temp_view' + params, {
      headers: new Headers({'Content-Type': 'application/json'}),
      method: 'POST',
      body: JSON.stringify(body)
    }).then(function (response) {
        ok = response.ok;
        status = response.status;
      return response.json();
    }).then(function (result) {
      if (!ok) {
        result.status = status;
        throw generateErrorFromResponse(result);
      }
      return result;
    }).then(postprocessAttachments(opts));
  }

params += (params[0] === '?' ? '&' : '?') + keysAsString;
      } else {
        method = 'POST';
        if (typeof fun === 'string') {
          body = {keys: opts.keys};
        } else { // fun is {map : mapfun}, so append to this
          fun.keys = opts.keys;
        }
      }
    }

    // We are referencing a query defined in the design doc
    if (typeof fun === 'string') {
      var parts = parseViewName(fun);
      return db.fetch('_design/' + parts[0] + '/_view/' + parts[1] + params, {
        headers: new Headers({'Content-Type': 'application/json'}),
        method: method,
        body: JSON.stringify(body)
      }).then(function (response) {
        ok = response.ok;
        status = response.status;
        return response.json();
      }).then(function (result) {
        if (!ok) {
          result.status = status;
          throw generateErrorFromResponse(result);
        }
        // fail the entire request if the result contains an error
        result.rows.forEach(function (row) {
          /* istanbul ignore if */
          if (row.value && row.value.error && row.value.error === "builtin_reduce_error") {
            throw new Error(row.reason);

function dbFetch(db, path, opts, callback) {
  var status, ok;
  opts.headers = new Headers({'Content-type': 'application/json'});
  db.fetch(path, opts).then(function (response) {
    status = response.status;
    ok = response.ok;
    return response.json();
  }).then(function (json) {
    if (!ok) {
      json.status = status;
      var err = generateErrorFromResponse(json);
      callback(err);
    } else {
      callback(null, json);
    }
  }).catch(callback);
}

function fetchJSON(url, options, callback) {

    var result = {};

    options = options || {};
    options.headers = options.headers || new Headers();

    if (!options.headers.get('Content-Type')) {
      options.headers.set('Content-Type', 'application/json');
    }
    if (!options.headers.get('Accept')) {
      options.headers.set('Accept', 'application/json');
    }

    return ourFetch(url, options).then(function (response) {
      result.ok = response.ok;
      result.status = response.status;
      return response.json();
    }).then(function (json) {
      result.data = json;
      if (!result.ok) {
        result.data.status = result.status;

function httpViewCleanup(db) {
    return db.fetch('_view_cleanup', {
      headers: new Headers({'Content-Type': 'application/json'}),
      method: 'POST'
    }).then(function (response) {
      return response.json();
    });
  }