Fixing unknown dependencies error for debounce and throttle

When working with React Hooks, particularly `useCallback` and `useMemo`, you might encounter the ESLint error: React Hook useCallback received a function whose dependencies are unknown. Pass an inline function instead react-hooks/exhaustive-deps

This error often arises when implementing debouncing or throttling in your components. In this article, we'll explore why this error occurs and how to resolve it effectively.

Understanding the Error

The error occurs because useCallback expects a function with clearly defined dependencies. When you pass a debounced or throttled function that returns another function, ESLint cannot determine its dependencies, leading to the warning.

Solution 1: Using a Custom `useDebounce` Hook with `useCallback`

Creating a custom hook ensures that the debounced function maintains the correct dependencies. Here's how you can implement it:

/**
 * @param {Function} func
 * @param {number} delay
 * @returns {Function}
 */
import { useCallback, useRef } from "react";

const useDebounce = (func, delay) => {
  const debounceRef = useRef();

  const debounce = useCallback(
    function () {
      const context = this;
      const args = arguments;
      clearTimeout(debounceRef.current);
      debounceRef.current = setTimeout(() => func.apply(context, args), delay);
    },
    [func, delay]
  );

  return debounce;
};

export default useDebounce;

import React, { useState } from "react";
import useDebounce from "./useDebounce";

const DebouncedSearch = () => {
  const [searchText, setSearchText] = useState("");

  /**
   * @param {string} e
   */
  const fetchData = (e) => {
    console.log(e, "Making an API call");
  };

  const debounce = useDebounce(fetchData, 2000);

  /**
   * @param {React.ChangeEvent<HTMLInputElement>} e
   */
  const handleChange = (e) => {
    setSearchText(e.target.value);
    debounce(e.target.value);
  };

  return (
    <div>
      <input type="text" onChange={handleChange} value={searchText} />
    </div>
  );
};

export default DebouncedSearch;

In this setup:

• useDebounce Hook: Encapsulates the debouncing logic and utilizes `useCallback` to memoize the debounced function.
• DebouncedSearch Component: Uses the custom hook to debounce the `fetchData` function, ensuring proper dependency management.

Solution 2: Leveraging `useMemo` for Debounced Functions

Alternatively, you can use useMemo to memoize the debounced function. This approach aligns with the ESLint requirement for inline functions.

import React, { useState, useMemo, useCallback } from "react";
import { debounce } from "lodash";

const Search = ({ onSearch }) => {
  const [value, setValue] = useState("");

  /**
   * @returns {Function}
   */
  const debouncedSearch = useMemo(
    () =>
      debounce((val) => {
        onSearch(val);
      }, 750),
    [onSearch]
  );

  /**
   * @param {React.ChangeEvent<HTMLInputElement>} e
   */
  const handleChange = useCallback(
    (e) => {
      setValue(e.target.value);
      debouncedSearch(e.target.value);
    },
    [debouncedSearch]
  );

  return <input type="text" value={value} onChange={handleChange} />;
};

export default Search;

In this example:

• useMemo Hook: Memoizes the debounced version of the `onSearch` function, ensuring it only recalculates when `onSearch` changes.
• handleChange Callback: Remains optimized by depending on the memoized `debouncedSearch`.

Conclusion

Handling debounced and throttled functions in React Hooks requires careful management of dependencies to satisfy ESLint rules. By either creating a custom debouncing hook with `useCallback` or utilizing `useMemo` to memoize the debounced function, you can effectively eliminate the unknown dependencies error.

Implementing these solutions ensures optimal performance and adherence to best practices in your React applications.