newsroom/node_modules/change-emitter/lib/index.js

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});
var createChangeEmitter = exports.createChangeEmitter = function createChangeEmitter() {
  var currentListeners = [];
  var nextListeners = currentListeners;

  function ensureCanMutateNextListeners() {
    if (nextListeners === currentListeners) {
      nextListeners = currentListeners.slice();
    }
  }

  function listen(listener) {
    if (typeof listener !== 'function') {
      throw new Error('Expected listener to be a function.');
    }

    var isSubscribed = true;

    ensureCanMutateNextListeners();
    nextListeners.push(listener);

    return function () {
      if (!isSubscribed) {
        return;
      }

      isSubscribed = false;

      ensureCanMutateNextListeners();
      var index = nextListeners.indexOf(listener);
      nextListeners.splice(index, 1);
    };
  }

  function emit() {
    currentListeners = nextListeners;
    var listeners = currentListeners;
    for (var i = 0; i < listeners.length; i++) {
      listeners[i].apply(listeners, arguments);
    }
  }

  return {
    listen: listen,
    emit: emit
  };
};