blog-post-introduction-to-redux-for-web-application-development-08.js

function createStore(reducer, preloadedState) {
  var currentState = preloadedState;
  // Keep track of all listeners
  var listeners = [];

  function getState() {
    return currentState;
  }

  // Subscribe new listeners to the store
  function subscribe(listener) {
    listeners.push(listener);
    
    // Provide method for removing the subscription
    return function unsubscribe() {
      var index = listeners.indexOf(listener);
      listeners.splice(index, 1);
    };
  }

  return {
    getState: getState,
    // Expose the API
    subscribe: subscribe
  };
}