Understanding Redux: Core Concepts, Store Mechanics, and Compose

Annoying Concepts

Developers new to Redux often encounter confusing terminology such as compose , applyMiddleware , and reducer in the official documentation, which can feel overwhelming. In practice, these abstractions are high‑level business logic that need not be presented to users up front.

dispatch: update state, trigger callbacks

The dispatch method is the core of the store. Its simplified implementation updates the current state via the reducer and then notifies all registered listeners. The function receives an action object, which determines how the state should change.

subscriber: register callbacks and clean up

The subscribe function adds a listener to nextListeners so that dispatch can invoke it later, and returns an unsubscribe function that removes the listener when the component is unmounted, preventing the common “setState on unmounted component” warning.

Core Kernel

Redux inherits the Flux store concept: a data container that provides dispatch , subscribe , and getState . While dispatch schedules state changes and subscribe listens to those changes, the reducer determines *how* the state is transformed.

action: a plain object

An action is a simple JavaScript object that must contain a type field. Different user interactions generate different actions (e.g., INCREMENT vs. DECREMENT ), and reducers handle each type to produce the new state.

reducer: composable state transformers

Reducers receive the current state and an action, returning a new state. Multiple reducers can be combined with combineReducers to build a single state tree while keeping each reducer focused on a specific slice of logic.

compose: functional programming glue

The compose utility lets developers chain functions in a right‑to‑left order, turning nested calls like a(b(c(d(e())))) into a more readable compose(a,b,c,d,e)(value) . This pattern becomes especially useful when implementing middleware.

Summary

The article demystifies Redux by showing that it is essentially a Flux‑style store augmented with reducers that can be freely combined, and a compose helper for functional composition. The next installment will cover middleware, the feature that has driven Redux’s widespread adoption.

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