CODEWITHSUNDEEP
javascriptreactjs
Arex Speed
Arex Speed

Reputation: 177

Bug with setInterval in React

What is wrong with this case. I want to display a random name and change it for every 2 seconds but after few seconds is changing continuously and look like the names are overwriting even when I clean the setName?

import React, {useState} from "react";
import "./styles.css";

export default function App() {
  const [name, setName] = useState();
    const arrayName = ['Tom','Alice','Matt','Chris'];
  
    const nameChange = () => {
        const rand = Math.floor(Math.random()*arrayName.length);
        setName(arrayName[rand])   
    }
    setInterval(()=>{ 
        setName('');
        nameChange();
        console.log(name);
    }, 2000)
  return (
    <div className="App">
      <h1>Hello {name}</h1>

    </div>
  );
}

Upvotes: 1

Views: 1151

Answers (3)

Constantin
Constantin

Reputation: 915

The issue is that you never do clearInterval. Whenever the component calls render, a new interval will issue.

Wrap setInterval in useEffect, which gets called when a component renders. The return of useEffectis a function that dictates what happens on component unmounting phase. See more here

useEffect(){
    const tmp = setInterval(()=>{ 
        setName('');
        nameChange();
        console.log(name);
    }, 2000)
    return () => { clearInterval(tmp); };
}

Upvotes: 2

Benjamin
Benjamin

Reputation: 3656

The issue is that every time your component is rendered, you are creating a new interval.

The solution is to wrap the setInterval call in useEffect, and then return a function to useEffect to clear the interval.

import React, { useState, useCallback, useEffect } from 'react';
import './styles.css';

const arrayName = ['Tom', 'Alice', 'Matt', 'Chris'];

export default function App() {
  const [name, setName] = useState();

  const nameChange = useCallback(() => {
    const rand = Math.floor(Math.random() * arrayName.length);
    setName(arrayName[rand]);
  }, [setName]);

  useEffect(() => {
    const intervalId = setInterval(() => {
      setName('');
      nameChange();
    }, 2000);

    return () => clearInterval(intervalId);
  }, [nameChange]);

  return (
    <div className="App">
      <h1>Hello {name}</h1>
    </div>
  );
}

Upvotes: 1

user14311453
user14311453

Reputation:

It's creating a new interval every time your component renders, which causes it to render again and you end up with an infinite loop.

Try this:

import React, {useState, useEffect, useCallback} from "react";
import "./styles.css";

const arrayName = ['Tom','Alice','Matt','Chris'];

export default function App() {
  const [name, setName] = useState();
  
  const nameChange = useCallback(() => {
    const rand = Math.floor(Math.random()*arrayName.length);
    setName(arrayName[rand])   
  }, []);

  useEffect(() => {
    const interval = setInterval(() => {  
      setName('');
      nameChange();
    }, 2000)
    return () => clearInterval(interval)
  }, [nameChange]);

  return (
    <div className="App">
      <h1>Hello {name}</h1>

    </div>
  );
}

Upvotes: 3

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