Is it possible to fetch API without useEffect in React JS?-CodePudding

Hello i'm newbie here... I found my friend's code when he using useState instead of using useEffect to fetch the API. I tried it and it worked, the code didn't cause an error and infinite loops.

here is for the code

import { useState } from "react";
import { IN_THEATER, POSTER } from "../../../constant/movies";
import { GlobalGet } from "../../../utilities/fetch";

const Service = () => {
  const [movieData, setMovieData] = useState({ data: null, poster: null });

  const fetchMovieData = async () => {
    try {
      let movieRes = await GlobalGet({ url: `${IN_THEATER}` });
      return movieRes;
    } catch (error) {
      console.log(error);
    }
  };

  const fetchPoster = async () => {
    try {
      let posterRes = await GlobalGet({ url: `${POSTER}` });
      return posterRes;
    } catch (error) {
      console.log(error);
    }
  };

  const fetchData = async () => {
    setMovieData({
      data: await fetchMovieData(),
      poster: await fetchPoster(),
    });
  };

  useState(() => { //<=here it is
    fetchData();
  }, []);
  return {
    movieData,
  };
};

export default Service;

And my question is, why it could be happen ? why using useState there doesn't cause infinite an infinite loops ?

CodePudding user response：

The useState() function can accept an initializer function as its first argument:

const [state, setState] = useState(initializerFunction)

When a function is passed to useState(), that function is only called once before the component initially mounts. In your case below, the initializer function is an anonymous arrow function:

useState(() => { // <-- Initializer function invoked once
  fetchData();
}, []);

Here, the initializer function is () => { fetchData(); }, which is invoked once before the initial mount, so the fetchData() method is only called once. The array that is passed as the second argument [] is useless and doesn't do anything in this case as it's ignored by useState(). The above useState would behave the same if you did useState(fetchData);. Because fetchData() is only called once on the initial mount, any state updates of your component don't cause the fetchData() function to execute again as it's within the initializer function.

With that said, useState() shouldn't be used for fetching data on mount of your component, that's what useEffect() should be used for instead.

CodePudding user response：

Generally it's possible to fetch data from outside of the useEffect hook.

Somewhere in the body of your component...

const [fetchedData, setFetchedData] = useState(false)

const someFetchFunc = asyunc (url) => {

setFetchedData(!fetchedData)

const res = await fetch(url)
const data = await res.json()
setMovieData(data)

}

!fetchedData && someFetchFunc()

But this is an antipattern. In this case developer lacks a whole toolset of dealing with possible issues. What if fetching fails?

So, it's generally a good idea to handle all the side effects like fetching in a place that was intended for that. It's useEffect hook)

CodePudding user response：

useState returns a tuple [stateVariable, setterFunction]. You can see its typical use at the top of your component:

  const [movieData, setMovieData] = useState({ data: null, poster: null });

This code block:

useState(() => { //<=here it is
    fetchData();
  }, []);
  return {
    movieData,
  };

isn't causing an infinite loop because it's not actually setting any state (which would cause a re-render), it's just calling the useState function (again, which returns a state variable and a setter function) and not assigning its result to a variable.

In addition to that, this code has a bunch of problems. I'd start by reading up on the basics of React Hooks.