React Fetch API 在页面加载时被调用 2 次

Question

React Fetch API Being Called 2 Times on page load, I don't know what is missing in this code or what I am doing wrong. I have faced this problem from the morning, I really appreciate any help you can provide. React Fetch API Being Called 2 Times on page load, I don't know what is missing in this code or what I am doing wrong. I face this problem from the morning, I really appreciate any help you can provide.

import React, { useState, useEffect } from 'react'
    import axios from 'axios';
    import {  Grid, Paper, TextField } from '@mui/material'
    import PersonOutlineIcon from '@mui/icons-material/PersonOutline';
    
    function FormApi() {
    
      //Mui fileds and paper style
      const paperStyle = { padding: '50px ', width: 550, margin: '50px auto' }
    
      //Fetch data from api
      const [userx, setUserx] = useState([{data:null,support:null}]);
      const url = 'https://reqres.in/api/users/2';
    
        useEffect(()=>{
    
          //debugger
    
          const fetchData = async () =>{
    
            await axios.get(`${url}`)
            .then((response) =>{
              setUserx(response.data)
    
            }).catch((error)=>{
                console.log(error)
            })
          }
    
          fetchData();
          }
    
        ,[]);
    
      return (
    
        <Grid container spacing={2} style={paperStyle}>
    
          <Grid align='center' >
            <Paper elevation={20} >
    
              <Grid align='center'>
    
                <h2 style={{padding:'10px' ,background: "#000080", color: 'white' }}> 
       <PersonOutlineIcon large style={{fontSize:'80%'}} />User Details</h2>
    
              </Grid>
              
              <form>
             
              <img style={{width:"20%"}} src={userx.data  ? userx.data.avatar : ''}/>
                <h1 style={{color:'#000080'}}>{userx.data  ? userx.data.first_name : ''} 
       {userx.data  ? userx.data.last_name : ''}</h1>
    
              <Grid container >
                <Grid item xs={6} >
                  <h2 style={{color:'white', background: "purple"}}>Contact Info</h2>
                  <TextField   value={userx.data  ? userx.data.id : ''}   variant="standard" 
         />
                  <TextField  value={userx.data  ? userx.data.email  : ''}   
       variant="standard" />
                </Grid>
    
                <Grid item align='left' xs={6} style={{marginBottom:'40px'}}>
                  <h2 style={{color:'white', background: "purple"}}>Social Link</h2>
                  <TextField  value={userx.support ? userx.support.url : ''}   
       variant="standard" />
                  <TextField  value={userx.support ? userx.support.text : ''}     
      variant="standard" />
                </Grid>
                
              </Grid>
              </form>
            </Paper>
          </Grid>
        </Grid>       
      )
    }enter code here
    
    export default FormApi

Answer 1

This is normal behaviour in React 18 . It will only be done on development environments and when StrictMode is enabled and will not be a problem in your production Build.

A bit annoying, but nothing really to worry about. There is a workaround which you can learn more about in a in-depth answer here: React 18, useEffect is getting called two times on mount

Answer 2

as much as I know, this issue is caused by the HTTTP client sending 2 request, one to the route path "/" and the other to "/favicon.ico"

make this change :

useEffect(()=>{ checkLocation(); //your code ,[]);

Answer 3

after some revision try this

function FormApi() {

  //Mui fileds and paper style
  const paperStyle = { padding: '50px ', width: 550, margin: '50px auto' }

  //Fetch data from api
  const [userx, setUserx] = useState([{data:null,support:null}]);
  const url = 'https://reqres.in/api/users/2';
//debugger

      const fetchData = async () =>{

        await axios.get(`${url}`)
        .then((response) =>{
          setUserx(response.data)

        }).catch((error)=>{
            console.log(error)
        })
      }

    useEffect(()=>{

      
      fetchData();
      }

    ,[]);

Answer 4

You can handle it with useRef hook:

const renderAfterCalled = useRef(false);

useEffect(() => {
    if (!renderAfterCalled.current) {
      // your API call func
    }

    renderAfterCalled.current = true;
}, []);

Answer 5

It's because React renders components 2 times in the development environment. To avoid this, you can comment out the <React.StrictMode> tag in index.js file.

Rendering twice will only appear in the development environment and StrictMode has many benefits for development:

• Identifying components with unsafe lifecycles
• Warning about legacy string ref API usage
• Warning about deprecated findDOMNode usage
• Detecting unexpected side effects
• Detecting legacy context API
• Ensuring reusable state

So it's better to keep the <React.StrictMode> tag if it doesn't affect your normal development work.

See also: React StrictMode