packages/node_modules/pouchdb-replication/src/replication.js

import { EventEmitter as EE } from 'events';
import inherits from 'inherits';

// We create a basic promise so the caller can cancel the replication possibly
// before we have actually started listening to changes etc
inherits(Replication, EE);
function Replication() {
  EE.call(this);
  this.cancelled = false;
  this.state = 'pending';
  var self = this;
  var promise = new Promise(function (fulfill, reject) {
    self.once('complete', fulfill);
    self.once('error', reject);
  });
  self.then = function (resolve, reject) {
    return promise.then(resolve, reject);
  };
  self.catch = function (reject) {
    return promise.catch(reject);
  };
  // As we allow error handling via "error" event as well,
  // put a stub in here so that rejecting never throws UnhandledError.
  self.catch(function () {});
}

Replication.prototype.cancel = function () {
  this.cancelled = true;
  this.state = 'cancelled';
  this.emit('cancel');
};

Replication.prototype.ready = function (src, target) {
  var self = this;
  if (self._readyCalled) {
    return;
  }
  self._readyCalled = true;

  function onDestroy() {
    self.cancel();
  }
  src.once('destroyed', onDestroy);
  target.once('destroyed', onDestroy);
  function cleanup() {
    src.removeListener('destroyed', onDestroy);
    target.removeListener('destroyed', onDestroy);
  }
  self.once('complete', cleanup);
};

export default Replication;