I am trying to render each element in the roles array. This code works in the timer (setInterval) is as follows:

1. Assigns the duplicate value of the state in let prevRole variable and its corresponding index in the let prevRoleIndex variable.

2. Renders the string of random characters 10 times iteratively with 50ms delay.

3. Now the next element in the roles array is assigned to let newRole variable, by adding 1 to previousRoleIndex and then updating the state with newRole variable.

import {useState, useEffect} from 'react'

const roles = ['Web Developer & UX Designer', 'Software Developer / Engineer', 'Blockchain Developer', 'Data Anaylist/ Scientist']

export default function App() {
 
    const [role, setRole] = useState(roles[0])
    const sleep = (value) =>{
        return new Promise(r => setTimeout(r, value));
    }
    const getRandomString = () =>{
        return (Math.random()).toString(36).substring(2);
    }
    useEffect(() => {
        const timer = setInterval(async() => {
            console.log("Timer has started")

            let prevRole = role;
            let prevRoleIndex = roles.findIndex((ele)=>ele===prevRole)
            
            console.log("Previous Role State: "  prevRole)
            
            for(let i=0; i<10; i  ){
                setRole(getRandomString())
                await sleep(50)
            }

            prevRoleIndex = prevRoleIndex 1 >= roles.length? -1: prevRoleIndex
            let newRole = roles[prevRoleIndex 1]
            
            console.log("New Role State: "  newRole)
            
            setRole(newRole)
          }, 3000);
          return () => clearInterval(timer);
        }, []);
        return(
          <div>
            <h1>{role}</h1>
          </div>
    )
}

The code works fine during first timer iteration and after second iteration the state does not update.

CodePudding user response：

Here's a working version: https://codesandbox.io/s/jolly-jones-05m65?file=/src/App.js

role in the timer was forever stuck at the first value.