React's useEffect hook function is often used in function components, and its functions are similar to componentDidMount , componentDidUpdate and componentWillUnmount methods in class components. useEffect will be executed when the component is rendered, which may be more times than you might think.
In a simple example, useEffect may only run once. But in complex applications, especially when props changes are involved, this is not guaranteed. The problem is that if you perform operations such as getting data from the API in useEffect , it can result in repeated fetching of data, which is both inefficient and unnecessary.
The solution lies in the second parameter of useEffect .
The second parameter is an array containing variables that the component needs to check to ensure that changes have occurred before re-rendering. You can put any props and state into here for checking.
Alternatively, you can pass in an empty array:
import React, { useEffect } from 'react';
function App() {
useEffect(() => {
// Execute only once, for example, get data from the API}, []);
Return (
<div>
{/* Use the obtained data*/}
</div>
);
}
This will ensure that useEffect only runs once.
Documentation description:
If you use this optimization, make sure the array contains all the values ??in the component scope that change over time and is used by useEffect (such as props and state). Otherwise, your code will reference an outdated value from a previous render.
The above is the detailed content of Run useEffect Only Once. 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)
Hot Topics
What is 'render-blocking CSS'?
Jun 24, 2025 am 12:42 AM
CSS blocks page rendering because browsers view inline and external CSS as key resources by default, especially with imported stylesheets, header large amounts of inline CSS, and unoptimized media query styles. 1. Extract critical CSS and embed it into HTML; 2. Delay loading non-critical CSS through JavaScript; 3. Use media attributes to optimize loading such as print styles; 4. Compress and merge CSS to reduce requests. It is recommended to use tools to extract key CSS, combine rel="preload" asynchronous loading, and use media delayed loading reasonably to avoid excessive splitting and complex script control.
External vs. Internal CSS: What's the Best Approach?
Jun 20, 2025 am 12:45 AM
ThebestapproachforCSSdependsontheproject'sspecificneeds.Forlargerprojects,externalCSSisbetterduetomaintainabilityandreusability;forsmallerprojectsorsingle-pageapplications,internalCSSmightbemoresuitable.It'scrucialtobalanceprojectsize,performanceneed
Does my CSS must be on lower case?
Jun 19, 2025 am 12:29 AM
No,CSSdoesnothavetobeinlowercase.However,usinglowercaseisrecommendedfor:1)Consistencyandreadability,2)Avoidingerrorsinrelatedtechnologies,3)Potentialperformancebenefits,and4)Improvedcollaborationwithinteams.
CSS Case Sensitivity: Understanding What Matters
Jun 20, 2025 am 12:09 AM
CSSismostlycase-insensitive,butURLsandfontfamilynamesarecase-sensitive.1)Propertiesandvalueslikecolor:red;arenotcase-sensitive.2)URLsmustmatchtheserver'scase,e.g.,/images/Logo.png.3)Fontfamilynameslike'OpenSans'mustbeexact.
What is Autoprefixer and how does it work?
Jul 02, 2025 am 01:15 AM
Autoprefixer is a tool that automatically adds vendor prefixes to CSS attributes based on the target browser scope. 1. It solves the problem of manually maintaining prefixes with errors; 2. Work through the PostCSS plug-in form, parse CSS, analyze attributes that need to be prefixed, and generate code according to configuration; 3. The usage steps include installing plug-ins, setting browserslist, and enabling them in the build process; 4. Notes include not manually adding prefixes, keeping configuration updates, prefixes not all attributes, and it is recommended to use them with the preprocessor.
What are CSS counters?
Jun 19, 2025 am 12:34 AM
CSScounterscanautomaticallynumbersectionsandlists.1)Usecounter-resettoinitialize,counter-incrementtoincrease,andcounter()orcounters()todisplayvalues.2)CombinewithJavaScriptfordynamiccontenttoensureaccurateupdates.
CSS: When Does Case Matter (and When Doesn't)?
Jun 19, 2025 am 12:27 AM
In CSS, selector and attribute names are case-sensitive, while values, named colors, URLs, and custom attributes are case-sensitive. 1. The selector and attribute names are case-insensitive, such as background-color and background-Color are the same. 2. The hexadecimal color in the value is case-sensitive, but the named color is case-sensitive, such as red and Red is invalid. 3. URLs are case sensitive and may cause file loading problems. 4. Custom properties (variables) are case sensitive, and you need to pay attention to the consistency of case when using them.
What is the conic-gradient() function?
Jul 01, 2025 am 01:16 AM
Theconic-gradient()functioninCSScreatescirculargradientsthatrotatecolorstopsaroundacentralpoint.1.Itisidealforpiecharts,progressindicators,colorwheels,anddecorativebackgrounds.2.Itworksbydefiningcolorstopsatspecificangles,optionallystartingfromadefin
