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import { useState, useEffect, useRef } from 'react';
// Usage
function App() {
// State and setters for ...
// Search term
const [searchTerm, setSearchTerm] = useState('');
// API search results
const [results, setResults] = useState([]);
// Searching status (whether there is pending API request)
const [isSearching, setIsSearching] = useState(false);
// Debounce search term so that it only gives us latest value ...
// ... if searchTerm has not been updated within last 500ms.
// The goal is to only have the API call fire when user stops typing ...
// ... so that we aren't hitting our API rapidly.
const debouncedSearchTerm = useDebounce(searchTerm, 500);
// Effect for API call
useEffect(
() => {
if (debouncedSearchTerm) {
setIsSearching(true);
searchCharacters(debouncedSearchTerm).then(results => {
setIsSearching(false);
setResults(results);
});
} else {
setResults([]);
}
},
[debouncedSearchTerm] // Only call effect if debounced search term changes
);
return (
<div>
<input
placeholder="Search Marvel Comics"
onChange={e => setSearchTerm(e.target.value)}
/>
{isSearching && <div>Searching ...</div>}
{results.map(result => (
<div key={result.id}>
<h4>{result.title}</h4>
<img
src={`${result.thumbnail.path}/portrait_incredible.${
result.thumbnail.extension
}`}
/>
</div>
))}
</div>
);
}
// API search function
function searchCharacters(search) {
const apiKey = 'f9dfb1e8d466d36c27850bedd2047687';
return fetch(
`https://gateway.marvel.com/v1/public/comics?apikey=${apiKey}&titleStartsWith=${search}`,
{
method: 'GET'
}
)
.then(r => r.json())
.then(r => r.data.results)
.catch(error => {
console.error(error);
return [];
});
}
// Hook
function useDebounce(value, delay) {
// State and setters for debounced value
const [debouncedValue, setDebouncedValue] = useState(value);
useEffect(
() => {
// Update debounced value after delay
const handler = setTimeout(() => {
setDebouncedValue(value);
}, delay);
// Cancel the timeout if value changes (also on delay change or unmount)
// This is how we prevent debounced value from updating if value is changed ...
// .. within the delay period. Timeout gets cleared and restarted.
return () => {
clearTimeout(handler);
};
},
[value, delay] // Only re-call effect if value or delay changes
);
return debouncedValue;
}
@AlexGalays

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commented Nov 9, 2018

No need to do that check {results &&
as you init the value with an empty array (which is nice)

@reddhouse

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commented Nov 10, 2018

Appreciate this example. As written, setResults(filteredResults) should be changed to setResults(results.data.results). Also consider using a key in your results.map(). Marvel provides a nice unique result.id you could use.

@gragland

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Owner Author

commented Nov 10, 2018

@AlexGalays @reddhouse All good suggestions, thanks! Updated the code :)

@taranvohra

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commented Mar 13, 2019

I feel theres a tiny bug here,

  // Effect for API call 
  useEffect(
    () => {
      if (debouncedSearchTerm) {
        setIsSearching(true);
        searchCharacters(debouncedSearchTerm).then(results => {
          setIsSearching(false);
          setResults(results);
        });
      } else {
        setResults([]);
      }
    },
    [debouncedSearchTerm] // Only call effect if debounced search term changes
  );

Let's say 2 API calls are made,
Call 1 at time X
Call 2 at time Y, (Y is greater than X)
If Call 2 resolves early and Call 1 resolves late, the latest results in the view will be of Call 1 whereas it should've been of Call 2. Here we need to commit only that result which was latest.

One way would be to use a ref,

 const latest = React.useRef(null);
  ...
  useEffect(
    () => {
      if (debouncedSearchTerm) {
        let now = latest.current = Date.now()
        setIsSearching(true);
        searchCharacters(debouncedSearchTerm).then(results => {
          if(now === latest.current) {
             setIsSearching(false);
             setResults(results);
          }
        });
      } else {
        setResults([]);
      }
    },
    [debouncedSearchTerm] // Only call effect if debounced search term changes
  );
@ArthurClemens

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commented Mar 15, 2019

Input's onChange is triggered by pressing Enter, which obviates the need for a debounce function. Using onInput makes more sense.

@AmaanKulshreshtha

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commented Jun 19, 2019

I have tried to replicate the original debounce function with the immediate flag here....don't know if this out of the scope for this particular hook or not

import React, { useRef, useEffect, useState } from "react";
import ReactDOM from "react-dom";

import "./styles.css";

/**
 * @description should display log message after 1 second
 */

function useDebounce(callback, time, immediate) {
  let args;
  const id = useRef();
  const initialState = useRef();
  initialState.current = true;

  const debounceFunction = () => {
    args = arguments;
  };

  useEffect(() => {
    if (!initialState.current) {
      const callNow = immediate && !id.current;
      const executeFuncLater = () => {
        id.current = null;
        if (!immediate) callback(args);
      };

      if (callNow) callback(args);
      id.current = setTimeout(executeFuncLater, time);
    }
    return () => {
      initialState.current = false;
      clearTimeout(id.current);
    };
  });

  return debounceFunction;
}

function App() {
  const [text, setText] = useState();
  const debounceFunction = useDebounce(
    () => {
      console.log("text", text);
    },
    500,
    true
  );

  const handleOnClick = () => {
    setText(text => text + "test1");
    debounceFunction(text);
  };

  return (
    <div className="App">
      <button onClick={handleOnClick}>Click Me</button>
      <h1>Hello CodeSandbox</h1>
      <h2>Start editing to see some magic happen!</h2>
      <h2>{text}</h2>
    </div>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

Link to the sandbox

Lemme know your feedback 😄 ✌️

PS: Works fine for a click example.....now making it work with the search example in the docs

@dsaftler

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commented Aug 16, 2019

The current sandbox of useDebounce does not render the image because it is missing an accessibilityLabel (alt): img elements must have an alt prop, either with meaningful text, or an empty string for decorative images. (jsx-a11y/alt-text) eslint This is in Chrome Version 76.0.3809.100.

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