Fixing Unknown Dependencies Error for Debounce and Throttle in React Hooks

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 inDebounce = useRef();

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

  return debounce;
};

export default useDebounce;

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

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

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

  const debounce = useDebounce(makeNetworkCall, 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 makeNetworkCall function, ensuring proper dependency management.

How This Solution Works

1. Dependency Management: The useDebounce hook explicitly declares its dependencies (func and delay) in the dependency array of useCallback, ensuring React's dependency tracking system understands what to watch.
2. Closure Preservation: By using useRef, we maintain access to the timeout reference across renders without triggering rerenders when it changes.
3. Context Preservation: The function uses this and arguments to preserve the execution context and all arguments passed to the debounced function.

This approach is particularly useful when:

• You need to debounce event handlers in forms
• You want to limit API calls during user input
• You're working in a component with frequent re-renders

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.

Benefits of the useMemo Approach

1. Library Integration: Leverages battle-tested libraries like Lodash, which often have more features and edge-case handling than simple custom implementations.
2. Cleaner Syntax: The useMemo approach can be more concise when working with library-provided debounce/throttle functions.
3. Consistent Memoization: Using useMemo follows React's preferred pattern for memoizing complex values.

The useMemo approach is ideal when:

• You're already using utility libraries like Lodash in your project
• You need advanced debounce features (like maxWait options)
• You want to minimize custom hook code in your project
• You need to handle the leading/trailing edge of function calls differently

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.

Happy Coding!