Home Web Front-end Front-end Q&A When does react's setstate synchronize?

When does react's setstate synchronize?

Jan 06, 2023 am 10:46 AM
react setstate

React's setstate is "synchronous" in native events and setTimeout, but "asynchronous" in synthetic events and hook functions; in React, if it is an event triggered by React, call setState will not update "this.state" synchronously, and other setState calls will execute "this.state" synchronously.

When does react's setstate synchronize?

The operating environment of this tutorial: Windows 10 system, react18.0.0 version, Dell G3 computer.

When will react's setstate be synchronized? When is it asynchronous?

Give the answer first:

Sometimes it appears asynchronous, sometimes it appears synchronous.

setState is "asynchronous" only in synthetic events and hook functions, and is synchronous in native events and setTimeout.

class Example extends React.Component {
  constructor() {
    super();
    this.state = {
      val: 0
    };
  }
  
  componentDidMount() {
    this.setState({val: this.state.val + 1});
    console.log(this.state.val);    // 第 1 次 log
    this.setState({val: this.state.val + 1});
    console.log(this.state.val);    // 第 2 次 log
    setTimeout(() => {
      this.setState({val: this.state.val + 1});
      console.log(this.state.val);  // 第 3 次 log
      this.setState({val: this.state.val + 1});
      console.log(this.state.val);  // 第 4 次 log
    }, 0);
  }
  render() {
    return null;
  }
};
Copy after login

1.setState is "asynchronous" only in synthetic events and hook functions, and is synchronous in native events and setTimeout.

2. The "asynchronous" of setState does not mean that it is internally implemented by asynchronous code. In fact, the execution process and code are all synchronous, but the calling sequence of synthetic events and hook functions is before updating.

As a result, the updated value cannot be obtained immediately in the synthetic event and hook function, forming the so-called "asynchronous". Of course, the updated value can be obtained through the callback in the second parameter setState(partialState, callback) result.

3. The batch update optimization of setState is also based on "asynchronous" (synthetic events, hook functions). There will be no batch updates in native events and setTimeout.

In "asynchronous" "If setState is performed multiple times on the same value, the batch update strategy of setState will overwrite it and take the last execution. If multiple different values ​​are setState at the same time, they will be merged and updated in batches during the update.

In React, if it is event processing triggered by React (such as event processing triggered by onClick), calling setState will not update this.state synchronously. Other setState calls will execute this synchronously. state. The so-called "in addition" refers to the event processing functions added directly through addEventListener, bypassing React, and the asynchronous calls generated through setTimeout/setInterval.

Reason:

In the implementation of React's setState function, a variable isBatchingUpdates will be used to determine whether to update this.state directly or put it in the queue and talk about it later, and isBatchingUpdates The default is false, which means that setState will update this.state synchronously. However, there is a function batchedUpdates. This function will change isBatchingUpdates to true. When React calls this batchedUpdates before calling the event processing function, the consequences are: That is, the event processing process setState controlled by React will not update this.state synchronously.

Please see https://github.com/LuNaHaiJiao/blog/issues/26

Recommended learning: "react video tutorial"

The above is the detailed content of When does react's setstate synchronize?. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Guide to React front-end and back-end separation: How to achieve decoupling and independent deployment of front-end and back-end Guide to React front-end and back-end separation: How to achieve decoupling and independent deployment of front-end and back-end Sep 28, 2023 am 10:48 AM

React front-end and back-end separation guide: How to achieve front-end and back-end decoupling and independent deployment, specific code examples are required In today's web development environment, front-end and back-end separation has become a trend. By separating front-end and back-end code, development work can be made more flexible, efficient, and facilitate team collaboration. This article will introduce how to use React to achieve front-end and back-end separation, thereby achieving the goals of decoupling and independent deployment. First, we need to understand what front-end and back-end separation is. In the traditional web development model, the front-end and back-end are coupled

How to build a reliable messaging app with React and RabbitMQ How to build a reliable messaging app with React and RabbitMQ Sep 28, 2023 pm 08:24 PM

How to build a reliable messaging application with React and RabbitMQ Introduction: Modern applications need to support reliable messaging to achieve features such as real-time updates and data synchronization. React is a popular JavaScript library for building user interfaces, while RabbitMQ is a reliable messaging middleware. This article will introduce how to combine React and RabbitMQ to build a reliable messaging application, and provide specific code examples. RabbitMQ overview:

React Router User Guide: How to implement front-end routing control React Router User Guide: How to implement front-end routing control Sep 29, 2023 pm 05:45 PM

ReactRouter User Guide: How to Implement Front-End Routing Control With the popularity of single-page applications, front-end routing has become an important part that cannot be ignored. As the most popular routing library in the React ecosystem, ReactRouter provides rich functions and easy-to-use APIs, making the implementation of front-end routing very simple and flexible. This article will introduce how to use ReactRouter and provide some specific code examples. To install ReactRouter first, we need

PHP, Vue and React: How to choose the most suitable front-end framework? PHP, Vue and React: How to choose the most suitable front-end framework? Mar 15, 2024 pm 05:48 PM

PHP, Vue and React: How to choose the most suitable front-end framework? With the continuous development of Internet technology, front-end frameworks play a vital role in Web development. PHP, Vue and React are three representative front-end frameworks, each with its own unique characteristics and advantages. When choosing which front-end framework to use, developers need to make an informed decision based on project needs, team skills, and personal preferences. This article will compare the characteristics and uses of the three front-end frameworks PHP, Vue and React.

Integration of Java framework and front-end React framework Integration of Java framework and front-end React framework Jun 01, 2024 pm 03:16 PM

Integration of Java framework and React framework: Steps: Set up the back-end Java framework. Create project structure. Configure build tools. Create React applications. Write REST API endpoints. Configure the communication mechanism. Practical case (SpringBoot+React): Java code: Define RESTfulAPI controller. React code: Get and display the data returned by the API.

How to use React to develop a responsive backend management system How to use React to develop a responsive backend management system Sep 28, 2023 pm 04:55 PM

How to use React to develop a responsive backend management system. With the rapid development of the Internet, more and more companies and organizations need an efficient, flexible, and easy-to-manage backend management system to handle daily operations. As one of the most popular JavaScript libraries currently, React provides a concise, efficient and maintainable way to build user interfaces. This article will introduce how to use React to develop a responsive backend management system and give specific code examples. Create a React project first

Vue.js vs. React: Project-Specific Considerations Vue.js vs. React: Project-Specific Considerations Apr 09, 2025 am 12:01 AM

Vue.js is suitable for small and medium-sized projects and fast iterations, while React is suitable for large and complex applications. 1) Vue.js is easy to use and is suitable for situations where the team is insufficient or the project scale is small. 2) React has a richer ecosystem and is suitable for projects with high performance and complex functional needs.

What closures does react have? What closures does react have? Oct 27, 2023 pm 03:11 PM

React has closures such as event handling functions, useEffect and useCallback, higher-order components, etc. Detailed introduction: 1. Event handling function closure: In React, when we define an event handling function in a component, the function will form a closure and can access the status and properties within the component scope. In this way, the state and properties of the component can be used in the event processing function to implement interactive logic; 2. Closures in useEffect and useCallback, etc.

See all articles