Question 412980 in Reactjs Question posted in
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How can a change take effect immediately ion reactjs?

I have an array called "results" and it has an array of object. I call a routine in reactjs

   const getdetails = () => {

   // api calls 

   setresults(results);
  }

Now when i run another routine for a drop down selection on change , it calls

     const handleSelectChange = async (event) => {
    console.log(results)
    const selectedGuid = event.target.value;
   };

The issue is that i need to use the result array and filter all id’s that are selectedGuid and then bind to a grid . But the console.log(results) shows that the results array is empty. Why is the array empty if earlier it had data ? How can i get this to go ?

I have tried to put it in useeffect but not sure if its right ?

UPDATE:

This is my api call to get the results

myService.getDetails(Id)
 .then(function (result) {
{ 
 //i fetch results 
 setresults(results);
}
Tags:

2

Answers


  1. 0

    The results array is empty because the state update hasn’t propagated by the time you’re logging it.
    We can resolve this by using useState() and useEffect() hooks to ensure the results array is set before running handleSelectChange.
    I have tried to give example of useEffect() below.

    Lets try modify getDetails() as below

    const getdetails = async () => {
    // api calls
    const fetchedResults = await apiCall();
    setResults(fetchedResults); // <=== ensure results are updated
};

    Lets define useEffect to look for changes in results array

    useEffect(() => {
    console.log("Updated results:", results);
}, [results]);

    Finally let’s update handleSelectChange()

    const handleSelectChange = (event) => {
    const selectedGuid = event.target.value;
    const filteredResults = results.filter(item => item.id === selectedGuid);
    console.log(filteredResults);
    // bind filteredResults to your grid here
};

    Edited and added sample component

    const DropDownComponent = () => {
    const [results, setResults] = useState([]);

    const getdetails = async () => {
        try {
            const result = await myService.getDetails(Id);
            setResults(result);
        } catch (error) {
            console.error("Error fetching details:", error);
        }
    };

    useEffect(() => {
        console.log("Results updated:", results);
    }, [results]);

    const handleSelectChange = (event) => {
        const selectedGuid = event.target.value;
        const filteredResults = results.filter(item => item.id === selectedGuid);
        console.log("Filtered Results:", filteredResults);
        // Bind filteredResults to your grid here
    };

    return (
        <select onChange={handleSelectChange}>
            {/* Your options here */}
        </select>
    );
};
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  2. 0

    The issue you’re encountering in React is due to how asynchronous state updates work in React and how closures capture variables within event handlers.

    Let me explain what’s happening here:
    When you call console.log(results) inside handleSelectChange, it’s logging the results state at the moment when the handler was created. React’s state setters like setResults are asynchronous, so calling setResults doesn’t immediately update the results array in subsequent synchronous code. Instead, it queues up the change, which React then applies in the next render cycle.

    You can learn more about this in react docs page.

    You can mitigate this issue by using useEffect. Here is how i would use useEffect to resolve this:

    1. Create a new state to store the filtered results based on the dropdown selection.
    2. Use useEffect to filter the results array every time results or selectedGuid changes.
    import { useState, useEffect } from "react";

const MyComponent = () => {
  const [results, setResults] = useState([]);
  const [filteredResults, setFilteredResults] = useState([]);
  const [selectedGuid, setSelectedGuid] = useState(null);


  const getDetails = () => {
    myService.getDetails(Id).then((result) => {
      setResults(result);
    });
  };


  const handleSelectChange = async (event) => {
    const selected = event.target.value;
    setSelectedGuid(selected);
  };

  // Filter results whenever `results` or `selectedGuid` changes
  useEffect(() => {
    if (selectedGuid && results.length) { // This case is to handle the empty state value during initial render
      const filtered = results.filter((item) => item.id === selectedGuid);
      setFilteredResults(filtered);
    }
  }, [results, selectedGuid]);

  return (
    <div>
      <select onChange={handleSelectChange}>
        {/* dropdown options */}
      </select>
      <GridComponent data={filteredResults} />
    </div>
  );
};

    Now this should ensure that your grid reflects the latest filtered data in response to both dropdown changes and new API data.

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