Redux reducers are core functions that manage application state changes. They take the current state and an action as input, and return a new state reflecting the action's effect. This ensures state immutability, a key principle in Redux for predictable and consistent behavior.
Why Redux? Redux leverages reducers to centralize state management within a single "store," providing a structured approach to state updates.
This guide focuses on understanding and working with reducer functions. We'll explore how they update application state and their crucial role within state management frameworks like Redux.
Understanding "State" in Redux
State represents the application's data at any given moment. Changes to state are triggered by user interactions (clicks, form submissions) or external events (network requests). In Redux, all state modifications occur exclusively within reducer functions. The reducer uses the current state and an action object to calculate the next state.
Mathematically:
Current State Action = New State
A reducer function typically looks like this:
const contactReducer = (state = initialState, action) => {
// State update logic
};
The initialState and action are defined by the application.
The state Parameter
The state parameter represents the application's current state. Initially, this is the initialState.
contactReducer(initialState, action);
For example, if our app starts with an empty contact list:
const initialState = { contacts: [] };
This initialState becomes the initial state parameter for the reducer.
The action Parameter
An action is an object with at least a type property indicating the type of state change. The payload property (optional) carries data needed for the update. For creating a new contact:
const action = {
type: 'NEW_CONTACT',
payload: {
name: 'John Doe',
location: 'Lagos, Nigeria',
email: 'john.doe@example.com'
}
};
action.type is essential; action.payload provides structured data.
Updating State Immutably
Directly modifying the state is forbidden. Use Object.assign() or the spread operator (...) to create a new state object.
Using Object.assign()
const contactReducer = (state, action) => {
switch (action.type) {
case 'NEW_CONTACT':
return Object.assign({}, state, {
contacts: [...state.contacts, action.payload]
});
default:
return state;
}
};
Object.assign({}, state, ...) creates a new object, copying state and adding/modifying properties. The empty object {} is crucial to avoid mutation.
Using the Spread Operator
Alternatively, the spread operator provides a more concise approach:
const contactReducer = (state, action) => {
switch (action.type) {
case 'NEW_CONTACT':
return { ...state, contacts: [...state.contacts, action.payload] };
default:
return state;
}
};
This cleanly adds the new contact to the existing contacts array without altering the original state.
The switch Statement
The switch statement handles different action.type values, directing the state update accordingly.
const contactReducer = (state, action) => {
switch (action.type) {
case 'NEW_CONTACT':
// ... (add contact logic)
break;
case 'UPDATE_CONTACT':
// ... (update contact logic)
break;
case 'DELETE_CONTACT':
// ... (delete contact logic)
break;
default:
return state; // Return unchanged state for unknown actions
}
};
The default case is crucial for handling unknown actions, preventing unexpected state changes.
A Complete Example (without Redux)
This demonstrates a reducer function in React (without Redux), showcasing the core principles:
// ... (React component code)
const [state, setState] = useState(initialState);
const handleNewContact = (contact) => {
const action = { type: 'NEW_CONTACT', payload: contact };
setState(contactReducer(state, action));
};
// ... (rest of component code)
This example shows how a reducer function can be used independently of Redux to manage state updates. Extending this to handle UPDATE_CONTACT is a straightforward exercise.
For more advanced Redux reducer usage, consult the official Redux documentation.
The above is the detailed content of Understanding How Reducers are Used in Redux. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
CSS tutorial for creating loading spinners and animations
Jul 07, 2025 am 12:07 AM
There are three ways to create a CSS loading rotator: 1. Use the basic rotator of borders to achieve simple animation through HTML and CSS; 2. Use a custom rotator of multiple points to achieve the jump effect through different delay times; 3. Add a rotator in the button and switch classes through JavaScript to display the loading status. Each approach emphasizes the importance of design details such as color, size, accessibility and performance optimization to enhance the user experience.
Addressing CSS Browser Compatibility issues and prefixes
Jul 07, 2025 am 01:44 AM
To deal with CSS browser compatibility and prefix issues, you need to understand the differences in browser support and use vendor prefixes reasonably. 1. Understand common problems such as Flexbox and Grid support, position:sticky invalid, and animation performance is different; 2. Check CanIuse confirmation feature support status; 3. Correctly use -webkit-, -moz-, -ms-, -o- and other manufacturer prefixes; 4. It is recommended to use Autoprefixer to automatically add prefixes; 5. Install PostCSS and configure browserslist to specify the target browser; 6. Automatically handle compatibility during construction; 7. Modernizr detection features can be used for old projects; 8. No need to pursue consistency of all browsers,
What is the difference between display: inline, display: block, and display: inline-block?
Jul 11, 2025 am 03:25 AM
Themaindifferencesbetweendisplay:inline,block,andinline-blockinHTML/CSSarelayoutbehavior,spaceusage,andstylingcontrol.1.Inlineelementsflowwithtext,don’tstartonnewlines,ignorewidth/height,andonlyapplyhorizontalpadding/margins—idealforinlinetextstyling
Styling visited links differently with CSS
Jul 11, 2025 am 03:26 AM
Setting the style of links you have visited can improve the user experience, especially in content-intensive websites to help users navigate better. 1. Use CSS's: visited pseudo-class to define the style of the visited link, such as color changes; 2. Note that the browser only allows modification of some attributes due to privacy restrictions; 3. The color selection should be coordinated with the overall style to avoid abruptness; 4. The mobile terminal may not display this effect, and it is recommended to combine it with other visual prompts such as icon auxiliary logos.
Creating custom shapes with css clip-path
Jul 09, 2025 am 01:29 AM
Use the clip-path attribute of CSS to crop elements into custom shapes, such as triangles, circular notches, polygons, etc., without relying on pictures or SVGs. Its advantages include: 1. Supports a variety of basic shapes such as circle, ellipse, polygon, etc.; 2. Responsive adjustment and adaptable to mobile terminals; 3. Easy to animation, and can be combined with hover or JavaScript to achieve dynamic effects; 4. It does not affect the layout flow, and only crops the display area. Common usages are such as circular clip-path:circle (50pxatcenter) and triangle clip-path:polygon (50%0%, 100 0%, 0 0%). Notice
How to create responsive images using CSS?
Jul 15, 2025 am 01:10 AM
To create responsive images using CSS, it can be mainly achieved through the following methods: 1. Use max-width:100% and height:auto to allow the image to adapt to the container width while maintaining the proportion; 2. Use HTML's srcset and sizes attributes to intelligently load the image sources adapted to different screens; 3. Use object-fit and object-position to control image cropping and focus display. Together, these methods ensure that the images are presented clearly and beautifully on different devices.
What are common CSS browser inconsistencies?
Jul 26, 2025 am 07:04 AM
Different browsers have differences in CSS parsing, resulting in inconsistent display effects, mainly including the default style difference, box model calculation method, Flexbox and Grid layout support level, and inconsistent behavior of certain CSS attributes. 1. The default style processing is inconsistent. The solution is to use CSSReset or Normalize.css to unify the initial style; 2. The box model calculation method of the old version of IE is different. It is recommended to use box-sizing:border-box in a unified manner; 3. Flexbox and Grid perform differently in edge cases or in old versions. More tests and use Autoprefixer; 4. Some CSS attribute behaviors are inconsistent. CanIuse must be consulted and downgraded.
Demystifying CSS Units: px, em, rem, vw, vh comparisons
Jul 08, 2025 am 02:16 AM
The choice of CSS units depends on design requirements and responsive requirements. 1.px is used for fixed size, suitable for precise control but lack of elasticity; 2.em is a relative unit, which is easily caused by the influence of the parent element, while rem is more stable based on the root element and is suitable for global scaling; 3.vw/vh is based on the viewport size, suitable for responsive design, but attention should be paid to the performance under extreme screens; 4. When choosing, it should be determined based on whether responsive adjustments, element hierarchy relationships and viewport dependence. Reasonable use can improve layout flexibility and maintenance.
