NGRX Workshop Notes - Meta-Reducers

• Intercept actions before they are reduced
• Intercept state before it is emitted
• Can change the control flow of the Store

Most common use cases

• Reset state when a signout action occurs
• for debugging creating logger
• to rehydrate when the application starts up

-It is like a plugin system for the store, they behave similarly to the interceptors

Example

An example of this can be to use it in a logger

const logger = (reducer: ActionReducer<any, any>) => (state: any, action: Action) => {
    console.log('Previous State', state);
    console.log('Action', action);

    const nextState = reducer(state, action);

    console.log('Next State', nextState);
    return nextState;
};

export const metaReducers: MetaReducer<State>[] = [logger];

Comments

[choubani amir]

How to understand this line ?
const logger = (reducer: ActionReducer) => (state: any, action: Action) => { }
There is two "=>".
Any idea ?

[Agafonov Vladislav]

function accepting reducer returns function that accepts state and action and returns new state?🤷‍♂️