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avoid useEffect to render at first load?


avoid useEffect to render at first load?

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avoid useEffect to render at first load?
Tag : javascript , By : Jarques
Date : January 11 2021, 03:34 PM

I hope this helps you . By default useEffect run first time and then on change of dependencies.
You can do this,
useEffect(() => {
    if(changeDataFlag){
      setData(
        data.map(o => ({
          id: "Titus",
          name: "Paul"
        }))
      );
    }
}, [changeDataFlag]);

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How to dispatch an redux action to load data inside useEffect on page load


Tag : reactjs , By : jehammon
Date : March 29 2020, 07:55 AM
To fix the issue you can do The problem here is that you are using incorrectly mapDispatchToProps. You don't need to set explicitly the dispatch function, that is what react redux does for you.
So, below is the correct way to do it:
// Now you won't be creating a new object every time your component re-renders
const mapDispatchToProps = {
  getRubrics: fetchRubrics
}

const Rubrics = (props) => {    
  const { getRubrics } = props;

  // You should always add elements inside your render scope
  // to the second array parameter of useEffect to prevent unexpected bugs.
  useEffect(() => {
      getRubrics();
  }, [getRubrics]);

  return (    
    <div>Your component here!</div>
  )
}

why is useEffect executing after each render?


Tag : javascript , By : Naveen
Date : March 29 2020, 07:55 AM
hope this fix your issue Im having problems with my effect hook. I only want it to render once. if I pass album.length or an empty array it returns an empty object. If the album is added as a dependency then the effect renders as an infinite loop. any help is appreciated.
import axios from 'axios';
import React, { useEffect, useState } from 'react';

function useAlbums() {
  const [albums, setAlbums] = useState([]);
  useEffect(() => {
    const fetchData = async () => {
      try {
        const { data } = await axios.get(
          'http://localhost:5000/api/albums/all',
        );
        setAlbums(data);
        console.log(albums);
      } catch (err) {
        console.log(err);
      }
    };
    fetchData();
  }, [albums]);

  return [albums, setAlbums];
}

const Component = () => {
  // use it in component
  const [albums] = useAlbums();

  return (
    <>
      {albums.map(({ _id }) => (
        <div key={_id}>{'add more content here'}</div>
      ))}
    </>
  );
};
const [albums, setAlbums] = useAlbums();

useEffect Hook Example: What causes the re-render?


Tag : reactjs , By : kgw
Date : January 02 2021, 06:48 AM
should help you out I'm going to do my best to explain(or walk through) what is happening. I'm also making two assumptions, in point 7 and point 10.
App component mounts. useEffect is called after the mounting. useEffect will 'save' the initial state and thus counter will be 0 whenever refered to inside it. The loop runs 3 times. Each iteration setCount is called to update the count and the console log logs the counter which according to the 'stored' version is 0. So the number 0 is logged 3 times in the console. Because the state has changed (0 -> 1, 1 -> 2, 2 -> 3) React sets like a flag or something to tell itself to remember to re-render. React has not re-rendered anything during the execution of useEffect and instead waits till the useEffect is done to re-render. Once the useEffect is done, React remembers that the state of counter has changed during its execution, thus it will re-render the App. The app re-renders and the useCounter is called again. Note here that no parameters are passed to the useCounter custom hook. Asumption: I did not know this myself either, but I think the default parameter seems to be created again, or atleast in a way that makes React think that it is new. And thus because the arr is seen as new, the useEffect hook will run again. This is the only reason I can explain the useEffect running a second time. During the second run of useEffect, the counter will have the value of 3. The console log will thus log the number 3 three times as expected. After the useEffect has run a second time React has found that the counter changed during execution (3 -> 1, 1 -> 2, 2 -> 3) and thus the App will re-render causing the third 'render' log. Asumption: because the internal state of the useCounter hook did not change between this render and the previous from the point of view of the App, it does not execute code inside it and thus the useEffect is not called a third time. So the first render of the app it will always run the hook code. The second one the App saw that the internal state of the hook changed its counter from 0 to 3 and thus decides to re-run it, and the third time the App sees the internal state was 3 and is still 3 so it decides not to re-run it. That's the best reason I can come up with for the hook to not run again. You can put a log inside the hook itself to see that it does not infact run a third time.

more than one setState in useEffect, how to aviod re-render?


Tag : javascript , By : mikhaelrasputin
Date : October 08 2020, 05:00 PM
I think the issue was by ths following , If you don't want to use useReducer, could could use Promise.all with your fetches
useEffect(()=>{
   const stateData = {}
   const fetch1 = axios.get('http://localhost:81/api/myapi/')
   const fetch2 = axios.get('http://localhost:81/api/mysecondapi/')
   Promise.all([fetch1, fetch2]).then(([res1,res2])=>{
     setName(res1.data['name']);
     setPrice(res1.data['price']);
     setColors(res2.data['colors']);
   })
 },[]);
Promise.all([fetch1, fetch2]).then(([res1, res2]) => {
  setNamePriceColor({ name: res1.data['name'],
    price: res1.data['price'],
    colors: res2.data['colors'] })
})

React: How to skip useEffect on first render


Tag : javascript , By : user96271
Date : October 03 2020, 03:00 AM
Hope this helps You can see this answer for an approach of how to ignore the initial render. This approach uses useRef to keep track of the first render.
  const firstUpdate = useRef(true);
  useLayoutEffect(() => {
    if (firstUpdate.current) {
      firstUpdate.current = false;
    } else {
     // do things after first render
    }
  });
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