Redux In Action
One way to solve this is to extract the shared state from the components, and put it into a centralized location outside the component tree. With this, our component tree becomes a big "view", and any component can access the state or trigger actions, no matter where they are in the tree!
Redux in Action
The type field should be a string that gives this action a descriptive name, like "todos/todoAdded". We usually write that type string like "domain/eventName", where the first part is the feature or category that this action belongs to, and the second part is the specific thing that happened.
A reducer is a function that receives the current state and an action object, decides how to update the state if necessary, and returns the new state: (state, action) => newState. You can think of a reducer as an event listener which handles events based on the received action (event) type.
A Redux reducer function is exactly the same idea as this "reduce callback" function! It takes a "previous result" (the state), and the "current item" (the action object), decides a new state value based on those arguments, and returns that new state.
We can say that Redux reducers reduce a set of actions (over time) into a single state. The difference is that with Array.reduce() it happens all at once, and with Redux, it happens over the lifetime of your running app.
The Redux store has a method called dispatch. The only way to update the state is to call store.dispatch() and pass in an action object. The store will run its reducer function and save the new state value inside, and we can call getState() to retrieve the updated value:
You can think of dispatching actions as "triggering an event" in the application. Something happened, and we want the store to know about it. Reducers act like event listeners, and when they hear an action they are interested in, they update the state in response.
This way, the UI won't accidentally overwrite data, and it's easier to trace why a state update happened. Since actions are plain JS objects, they can be logged, serialized, stored, and later replayed for debugging or testing purposes.
To specify how the state tree is updated based on actions, you write reducer functions. Reducers are pure functions that take the previous state and an action, and return the next state. Like any other functions, you can split reducers into smaller functions to help do the work, or write reusable reducers for common tasks.
Apart from this type attribute, the structure of an action object is totally up to the developer. It is recommended to keep your action object as light as possible and pass only the necessary information.
Action creators are the functions that encapsulate the process of creation of an action object. These functions simply return a plain Js object which is an action. It promotes writing clean code and helps to achieve reusability.
You can dispatch an action by directly using store.dispatch(). However, it is more likely that you access it with react-Redux helper method called connect(). You can also use bindActionCreators() method to bind many action creators with dispatch function.
Redux in Action is an accessible guide to effectively managing state in web applications. Built around common use cases, this practical book starts with a simple task-management application built in React. You'll use the app to learn the Redux workflow, handle asynchronous actions, and get your hands on the Redux developer tools. With each step, you'll discover more about Redux and the benefits of centralized state management. The book progresses to more-complex examples, including writing middleware for analytics, time travel debugging, and an overview of how Redux works with other frameworks such as Angular and Electron.
Using Redux in an existing React application
Handling side effects with the redux-saga library
Consuming APIs with asynchronous actions
Unit testing a React and Redux application
So, In the above reducer, a function created with two arguments first is the current state and next is the action we want to perform, First initialize the current state empty array because at first task list is gonna be empty. Then check the action type, different type of actions will have different functionality, In the above case if task is added, then it returns the array containing older list of task and with one new added, but the older state are not gonna mutate the older state we gonna return new one, this is needed to be kept in mind. Same for remove, if none of the above two then just return the list. Return the new state, Never mutate the older state. For more complex apps use combineReducers() to combine them so that it can pass to store.Store: The store is the object which holds the state of the application.Functions associated with Store:
Whenever a user adds an item to the cart, the application has to internally handle that action by adding that item to the cart object. It has to maintain its state internally and also show the user the total number of items in the cart in the UI.
State is Read-only in Redux. What makes Redux predictable is that to make a change in the state of the application, we need to dispatch an action which describes what changes we want to make in the state.
These actions are then consumed by something known as reducers, whose sole job is to accept two things (the action and the current state of the application) and return a new updated instance of the state.
So continuing with our above example of an e-commerce website, if the initial state of the cart is that it has 0 items, then an action of adding one item to the cart will increase the number of items in the cart by 1. And firing the action of adding one item to the cart again will increase the number of items in the cart to 2.
Given an initial state, with a specific list of actions in a specific order, it'll always provide us with the exact same final state of the entity. This is how Redux makes state management predictable.
On the click of the "Add to Cart" button, an action will be dispatched. This action is nothing but a JS object describing what changes need to be done in the store. Something like this:
Reducers, as the name suggests, take in two things: previous state and an action. Then they reduce it (read it return) to one entity: the new updated instance of state.
Whenever an action is dispatched, all the reducers are activated. Each reducer filters out the action using a switch statement switching on the action type. Whenever the switch statement matches with the action passed, the corresponding reducers take the necessary action to make the update and return a fresh new instance of the global state.
Also note that every reducer should handle the default case where, if none of the switch cases match with the passed action, then the reducer should return state as it is or perform any required logic on it before passing the state.
In the above example, on clicking the button, we had dispatched an action with an action creator called addItemToCart(). This action creator has dispatched an action with the type ADD_ITEM_TO_CART.
Next, we have created a reducer called cartReducer which takes the state (with the default initial state) and the action as parameters. It switches on the action type, and then whichever case matches with the dispatched action type, it makes the necessary update and returns the fresh new version of the updated state.
So in the above example, we first make a copy of the entire state using the spread operator ...state. Then we increment the noOfItemInCart by 1, update the cart array by adding the new object passed in the action.payload shown below, and then finally return the updated object.
The createAction helper combines these two declarations into one. It takes an action type and returns an action creator for that type. The action creator can be called either without arguments or with a payload to be attached to the action. Also, the action creator overrides toString() so that the action type becomes its string representation.
In many cases, you may want to write additional logic to customize the creation of the payload value, such as accepting multiple parameters for the action creator, generating a random ID, or getting the current timestamp. To do this, createAction accepts an optional second argument: a "prepare callback" that will be used to construct the payload value. 041b061a72