use promises to serialise access to an action

serialiser.js

// serialises access to an action
export default () => {
  // promise to allow the next action
  let next = Promise.resolve()
  return (action) => {
    let nextResolve
    const nextNext = () => new Promise(
      (resolve, reject) =>
        action()
          .then(
            (x) => {
              resolve(x)
              // allow next action
              nextResolve()
            },
          )
          .catch(reject),
    )
    const myNext = next
    next = new Promise(
      (resolve) => {
        nextResolve = resolve
      },
    )
    return myNext
      .then(nextNext)
  }
}