Redux is a lightweight state management library.
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Pro Borrows heavily from functional programming concepts
Redux's concepts are heavily influenced by functional programming languages. It is built on data immutability, and makes use of several functional programming features such as currying (usually seen in Redux middlewares).
Pro Changes to state are made with pure functions
Reducers are pure functions that returns the next state based on the previous state and an action (describing what should be changed). Since they are pure functions, they return a new state object instead of modifying the existing state. This ensures that it doesn't affect anything outside of the function's scope, making it free from unintended side effects and also makes debugging easier.
Pro Extremely lightweight
At only 2kB it's an extremely lightweight library.
Pro Lots of third-party resources online
Since it's such a popular library, there's plenty of tutorials, guides, or other third-party resources online.
Pro State is predictable
In Redux, the state of your application is held in a single object. The only way to change the state is to emit an action describing the change — there is no way to mutate state from the view, callbacks, or anywhere else. This makes the state of your application predictable and objective, and reduces the chances of any unintended state mutation by a callback somewhere else in your code.
Pro Can be used with many UI libraries/frameworks
Redux is most commonly used with React, but it can also be used with other UI libraries — Redux is strictly for state management only, thus it is agnostic to your front-end stack.
Pro Supports server-rendering
Redux supports server-rendering.
Con Steep learning curve
Redux's pattern can be unintuitive and hard to grasp, especially if you have not worked with functional languages before.