React 钩子使用效果

Question

I am having an issue with my app in that it re renders a new joke twice when I click the new button function. Here is my code:

    import React, { useState, useEffect } from "react";
import { Typography, Button } from "@material-ui/core";

import Navigation from "../Navigation";
export default function RandomJoke() {
  const [isLoaded, setLoaded] = useState(false);
  const [jokeData, setJokeData] = useState({});
  const [loadNewJoke, setLoadNewJoke] = useState(false);

  function useFetch() {
    async function fetchMyAPI() {
      let response = await fetch("https://icanhazdadjoke.com/slack");
      response = await response.json();
      setJokeData(response);
      setLoaded(true);
    }

    useEffect(() => {
      fetchMyAPI();
      if (loadNewJoke) setLoadNewJoke(false);
    }, [loadNewJoke]);
  }
  useFetch();

  function reloadJoke() {
    setLoaded(false);
    setLoadNewJoke(true);
  }

  return (
    <>
      <Navigation mainpage="RandomJoke" />

      <Typography variant="h6">Random Dad Joke</Typography>
      {isLoaded && <div>{jokeData.attachments[0].text}</div>}
      {!isLoaded && <div>loading...</div>}
      {isLoaded && (
        <Button variant="contained" onClick={() => reloadJoke()}>
          New one
        </Button>
      )}
    </>
  );
}

I tried adding a newjoke state hook but still couldn't work it out. Thank you

Answer 1

That useEffect fires whenever the value of loadNewJoke changes, right? Not just when loadNewJoke is set to true. Look closely at the calls made after a button press, and how many times setLoadNewJoke is called.

Answer 2

Try to move:

if (loadNewJoke) setLoadNewJoke(false);

In your fetchMyApi function. I'm guessing when you hit the button, you trigger the effect cuz u change you deps value in this case to true. Then before effect is over you change it again to false which will triggeer re-run on your effect. But why you dont just trigger fetchApi in your callback on button click, this way you can remove 1 state [loadNewJoke, setLoadNewJoke], will also remove the useEffect and make code cleaner over all

Answer 3

You're using useEffect wrong, i suggest u take a look at the Rules of Hooks

Don't call Hooks inside loops, conditions, or nested functions.

Answer 4

I followed what Andom Miltev said about triggering the async function directly in my callback and it now works smoothly - thank you everyone for the help :)

    import React, { useState, useEffect } from "react";
import { Typography, Button } from "@material-ui/core";

import Navigation from "../Navigation";
export default function RandomJoke() {
  const [isLoaded, setLoaded] = useState(false);
  const [jokeData, setJokeData] = useState({});

  async function fetchMyAPI() {
    setLoaded(false);
    let response = await fetch("https://icanhazdadjoke.com/slack");
    response = await response.json();
    setJokeData(response);
    setLoaded(true);
    console.log("fired 1");
  }

  useEffect(() => {
    fetchMyAPI();
  }, []);

  return (
    <>
      <Navigation mainpage="RandomJoke" />

      <Typography variant="h6">Random Dad Joke</Typography>
      {isLoaded && <div>{jokeData.attachments[0].text}</div>}
      {!isLoaded && <div>loading...</div>}
      {isLoaded && (
        <Button variant="contained" onClick={() => fetchMyAPI()}>
          New one
        </Button>
      )}
    </>
  );
}