Composing Middleware

In Redux, we can compose multiple middleware functions together to create more complex behavior. This allows us to enhance the capabilities of our Redux store and handle a wide range of scenarios.

When we talk about composing middleware, it means applying multiple middleware functions in a sequence. Each middleware function can modify, intercept, or dispatch actions before they reach the reducers.

One approach to composing middleware is through the use of a higher-order function. In this approach, each middleware function is a function that takes the store and returns another function that takes the next function in the middleware chain, which ultimately takes the action.

Here's an example of composing logger and thunk middleware:

1const logger = store => next => action => {
2  console.log('Dispatching:', action);
3  const result = next(action);
4  console.log('New State:', store.getState());
5  return result;
6};
7
8const thunk = store => next => action => {
9  if (typeof action === 'function') {
10    return action(store.dispatch, store.getState);
11  }
12
13  return next(action);
14};
15
16const middleware = [logger, thunk];
17
18const applyMiddleware = (store, middleware) => {
19  middleware.reverse().forEach(middlewareItem => {
20    store.dispatch = middlewareItem(store)(store.dispatch);
21  });
22};
23
24applyMiddleware(store, middleware);

In this example, we have two middleware functions: logger and thunk. The logger middleware logs the dispatched action and the new state after each action. The thunk middleware enables handling of function actions, allowing actions to be asynchronous or have side effects.

To compose the middleware, we create an array middleware with the desired order of middleware functions. Then, using the applyMiddleware function, we apply the middleware functions to the store by iterating over the array in reverse order.

This method ensures that each middleware function wraps the next middleware function, creating a chain that the action passes through. The final result is a composed chain of middleware functions that can handle different logic and modifications at each step.

When you compose middleware effectively, you're able to harness the power of Redux middleware to handle complex scenarios and implement advanced features in your application.

xxxxxxxxxx

const logger = store => next => action => {

  console.log('Dispatching:', action);

  const result = next(action);

  console.log('New State:', store.getState());

  return result;

};

​

const thunk = store => next => action => {

  if (typeof action === 'function') {

    return action(store.dispatch, store.getState);

  }

​

  return next(action);

};

​

const middleware = [logger, thunk];

​

const applyMiddleware = (store, middleware) => {

  middleware.reverse().forEach(middlewareItem => {

    store.dispatch = middlewareItem(store)(store.dispatch);

  });

};

​

applyMiddleware(store, middleware);