redux saga takeLatestPerActionAttr more specific takeLatest

takeLatestPerActionAttr.js

/*
 * Custom variant on redux saga's takeLatest that allows us to resolve race condition for data updates
 * based on something more specific than just the action type.
 * This accepts an action type (e.g. FETCH_DATA) as well as a fn that that extracts a value from the action
 * itself.  (e.g. (a) => a.module.id) to get action attribute value.  We can then effectively do a takeLatest for the action+value
 * combination and ensure that only the latest action for each combo isn't cancelled.
 * */
export const takeLatestPerActionAttr = (actionType, attrFn, saga, ...args) =>
  fork(function*() {
    const lastTasks = {}
    while (true) {
      const action = yield take(actionType)
      const attrVal = attrFn(action)
      const lastTask = lastTasks[attrVal]
      if (lastTask) {
        yield cancel(lastTask) // cancel is no-op if the task has already terminated
      }
      lastTasks[attrVal] = yield fork(saga, ...args.concat(action))
    }
  })