Identifying Changed Dependencies in UseEffect

Developing in React brings its set of challenges, especially when dealing with side effects in functional components. React's useEffect hook is a powerful tool for handling side effects, but it can sometimes be a mystery figuring out which dependency change triggered a particular effect.

To address this, let's introduce a practical solution: the useEffectDependencyDebugger.

The Motivation Behind useEffectDependencyDebugger While working with useEffect, developers often need to know exactly which dependency caused the hook to fire. This knowledge is crucial for debugging and optimization, particularly in complex components where effects depend on multiple state variables or props.

How useEffectDependencyDebugger Works The useEffectDebugger is a custom hook designed to wrap around the standard useEffect hook, providing clear insights into which dependencies have changed and triggered the effect. It leverages a helper hook, usePrevious, to track the previous values of dependencies, allowing for a comparison with their current values.

Building the Tools: usePrevious and useEffectDependencyDebugger

The usePrevious Hook:

const usePrevious = (value, initialValue) => {
  const ref = useRef(initialValue);
  useEffect(() => {
    ref.current = value;
  return ref.current;

usePrevious captures and retains the previous value of a dependency across renders. It utilizes useRef to hold the value and updates it on each render through useEffect.

The useEffectDependencyDebugger Hook:

const useEffectDependencyDebugger = (effectFunction, dependencies) => {
  const previousDependencies = usePrevious(dependencies, []);
  const changedDependencies = dependencies.reduce((accum, dependency, index) => {
    if (dependency !== previousDependencies[index]) {
      const keyIdx = index;
      accum[keyIdx] = { before: previousDependencies[index], after: dependency };
    return accum;
  }, {});

  if (Object.keys(changedDependencies).length) {
    console.log('[use-effect--dependency-debugger]', changedDependencies);

  useEffect(effectFunction, dependencies);

This custom hook identifies and logs the dependencies that have changed since the last render. It does so by comparing the current dependencies against their previous values, captured by usePrevious. Changes are then logged for debugging purposes, before calling the original useEffect hook with the provided effect function and dependencies.

Before :

useEffect(() => {
  // Effect logic here...
}, [dep1, dep2]);


useEffectDependencyDebugger(() => {
  // Effect logic here...
}, [dep1, dep2]);

Conclusion The useEffectDebugger offers a simple yet effective way to pinpoint which dependencies trigger the useEffect hook, significantly easing the debugging process. By providing insights into dependency changes, developers can better understand and optimize their components, leading to more efficient and maintainable React applications.