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Create a sleep function in React:

1. Define a function that takes a number of milliseconds as a parameter.
2. The function should return a PromisePromise that resolves after the provided number of milliseconds.

import {useEffect} from 'react';

const sleep = ms => new Promise(
  resolve => setTimeout(resolve, ms)
);

const App = () => {
  const handleClick = async event => {
    console.log('迹忆客');

    await sleep(1000);

    console.log('jiyik.com');
  };

  useEffect(() => {
    async function fetchData() {
      console.log('迹忆客');

      await sleep(1000);

      console.log('jiyik.com');
    }

    fetchData();
  });

  return (
    <div>
      <button onClick={handleClick}>Click</button>
    </div>
  );
};

export default App;

We create a sleepfunction that waits N milliseconds before returning.

const sleep = ms => new Promise(
  resolve => setTimeout(resolve, ms)
);

The function takes the number of milliseconds as a parameter and uses setTimeoutthe method to wait the specified number of milliseconds before resolving the Promise.

This function returns a Promise, so in order to use it, we must precede it with awaitthe keyword or use .then()the syntax.

We handleClickmark the function as asynchronous so we can use the keyword within it await.

const handleClick = async event => {
  console.log('迹忆客');

  await sleep(1000);

  console.log('jiyik.com');
};

The function starts logging to the console, then sleeps for 1 second and the logging ends.

useEffectThe same approach can be used inside the hook, but we cannot useEffectmark the function passed to as async.

useEffect(() => {
  async function fetchData() {
    console.log('迹忆客');

    await sleep(1000);

    console.log('jiyik.com');
  }

  fetchData();
});

Async functions return a Promiseobject, but useEffectthe hook can only return a cleanup function, so we have to useEffectdefine our async function in .