ReactJS Q & A


What are actions and reducers in Redux?

In the Redux architecture, actions and reducers are foundational elements that facilitate the deterministic and predictable management of the application’s state. Together, they provide a structured way to describe and handle changes to the state.

Actions in Redux are plain JavaScript objects that represent information about an event or a change that should take place in the application. Every action must have a `type` property, which typically is a string constant that gives a clear, readable description of the event, like `’ADD_TODO’` or `’UPDATE_USER’`. Actions can also carry additional data required to process the event, often encapsulated within a `payload` property. For example, an action to add a to-do might look like `{ type: ‘ADD_TODO’, payload: { text: ‘Learn Redux’ } }`. Actions are dispatched in response to user interactions, API calls, or other events, signaling the intent to transform the state in a specific manner.

Reducers, on the other hand, are pure functions that determine how the application’s state should change in response to an action. A reducer takes in two arguments: the current state and an action. It then returns the next state based on the action’s type and, if applicable, its payload. Crucially, reducers do not modify the existing state; instead, they produce a new state object, ensuring the state’s immutability. For example, in response to the `’ADD_TODO’` action, a to-do reducer might return a new array of to-dos with the new item appended. 

The beauty of reducers lies in their predictability. For any given state and action, a reducer will always produce the same output. This determinism makes state transitions transparent and testable.

While actions articulate “what happened” in a Redux application, reducers specify “how the state should change” in response. Their collaboration ensures a consistent and unidirectional flow of data, making state management in Redux applications systematic and maintainable.