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While React.js gives us stateful components, we need another isomorphic tool to manage state across our entire single-page-applications. More specifically we need a Single Source of Truth. Managing state in a declarative framework like React is critical, and easy to get wrong. How can we minimize side effects, while maximizing testability and reproducibility? We separate data, logic, and rendering. How can we visualize the changes we are pushing to our state? Uni-directional data flow makes it easy to reason about the interractions between actors.


Redux is a tiny (2kb) library used most commonly with React single-page-applications, to manage its state. It has an excellent browser dev tool that shows you the actions you make, and the state mutations that are caused by them.

Redux uses a single source of truth, called "the store", which is an immutable object tree. The only way to change the data is by emitting "actions", which describe what you want to do. These actions use "reducers" to perform the mutations to the state. All of these concepts are rooted in functional programming, and therefore highly unit testable.

Function React With react-redux Server
Presentation View React Components Client API
Communication Action Function Invocation
Logic to massage data for Storage Saga Services
Data Storage Store Database


Our TELUS isomorphic starter kit defines our standard UI application, with React and Redux at its heart. The FAQ has a lot of information about how we use Redux.

React Component

  1. Responsible for Presentation and User Interractions.
  2. It is blind to the complexities of the app (Doesn't know what happens after action is broadcasted).
  3. React to state change via connect.


  1. Responsible for Communication between parts of redux
  2. Use event descrption instead of function Invocation
  3. Listeners are responsible to determine how to react to actions

Reactive Style

  1. Describe an event via Actions-
  2. Actions describes a need as a fact or an event already happened without dictating how to fulfill the need.
  • personOneSaga reacts by => startWalking()
  • personTwoSaga reacts by => callTaxi()


  1. Responsible for application state (immutability, persisting to disk, etc).
  2. The Single Source of Truth.
  3. Keeper of state information, should not keep business logic.
  4. Can only be affected by actions.
  5. Prevent unintentional modifications by other methods via Object Reference, or Directly Accessing Store Members.
export const people = (state = [], action) => {
  switch (action.type) {
    case 'PERSON_REMOVED':
      return state.filter(person => !== action.payload);
      return state;

The Saga Library

  1. Responsible for Business Logic and Async actions (HTTP Calls).
  2. Does not keep local state.
  3. Typical use is take user input, make an HTTP call, and provide output to go into the store.

Redux Dataflow


Front-end developers