I ended up taking a little bit from various answers to make my own hook for this. I wanted the ability to just drop something in place of useEffect for quickly debugging what dependency was triggering useEffect.
const usePrevious = (value, initialValue) => {
const ref = useRef(initialValue);
useEffect(() => {
ref.current = value;
});
return ref.current;
};
const useEffectDebugger = (effectHook, dependencies, dependencyNames = []) => {
const previousDeps = usePrevious(dependencies, []);
const changedDeps = dependencies.reduce((accum, dependency, index) => {
if (dependency !== previousDeps[index]) {
const keyName = dependencyNames[index] || index;
return {
...accum,
[keyName]: {
before: previousDeps[index],
after: dependency
}
};
}
return accum;
}, {});
if (Object.keys(changedDeps).length) {
console.log('[use-effect-debugger] ', changedDeps);
}
useEffect(effectHook, dependencies);
};
Below are two examples. For each example, I assume that dep2 changes from 'foo' to 'bar'. Example 1 shows the output without passing dependencyNames and Example 2 shows an example with dependencyNames.
Example 1
Before:
useEffect(() => {
// useEffect code here...
}, [dep1, dep2])
After:
useEffectDebugger(() => {
// useEffect code here...
}, [dep1, dep2])
Console output:
{
1: {
before: 'foo',
after: 'bar'
}
}
The object key '1' represents the index of the dependency that changed. Here, dep2 changed as it is the 2nd item in the dependency, or index 1.
Example 2
Before:
useEffect(() => {
// useEffect code here...
}, [dep1, dep2])
After:
useEffectDebugger(() => {
// useEffect code here...
}, [dep1, dep2], ['dep1', 'dep2'])
Console output:
{
dep2: {
before: 'foo',
after: 'bar'
}
}
useEffects(one for each changing variable that may change independently). Because it's clear you're trying to couple two use cases into one?