use-what-changed

A tool and utility to debug major React hooks

Better than console logs and debugger

Don't believe. Try this codesandbox

React | React native | React with Electron

Debug following hooks

useEffect | useCallback | useMemo | useLayoutEffect | Custom hooks using core hooks

Working Example

Open the codesandbox link and see the console. You can uncomment the other hooks, and see the console accordingly, when the value changes across rerenders.

codesandbox use-what-changed example

Install

If you use yarn. Run

yarn add @simbathesailor/use-what-changed --dev

If you use npm. Run


npm i @simbathesailor/use-what-changed --save-dev

Motivation

I have been working on hooks for quite a long time. I use react hooks every day in my open source projects and also at work.

Now, using useEffect, useCallback, useMemo have really helped me compose the logic well together. But when the dependency list gets long. When I say long , it can be any thing greater than 3 for me and can be more or less for others.

With these large dependency array, I found it really difficult to debug and find out what is causing my useEffect to run again( same for useCallback and useMemo). I know two strategies to debug:

Break the useEffect logic into multiple useEffect. It is still fine, but expertise and time constraints will be there. People will not break the useEffect logic into smaller pieces first, they will try to spend time using logging the values and adding debugger so that not to change the production code.

Make use of usePrevious hook which can be defined something like this

import React from 'react';

function usePrevious(value) {
  const ref = React.useRef(value);

  React.useEffect(() => {
    ref.current = value;
  });

  return ref.current;
}

export default usePrevious;

And can be consumed like this:

const previousA = usePrevious(a);

const previousB = usePrevious(b);

const previousC = usePrevious(c);

useEffect(() => {
  if (previousA !== a) {
    console.log(`a has changed from ${previousA} to ${a}`);
  }

  if (previousB !== b) {
    console.log(`a has changed from ${previousB} to ${b}`);
  }

  if (previousC !== c) {
    console.log(`a has changed from ${previousC} to ${c}`);
  }
}, [a, b, c]);

However we can do it , it quite too much of work every time you run in the issue , where useEffect callback is running unexpectedly.

You are coming to an unknown code base, This plugin can really enhance your developer experience when working with hooks. It can give you a strong confidence while you make changes to existing hooks.

Even if you are coming to your own code after days. It becomes very difficult to wrap you head around various multiple hooks . This library with babel plugin helps you to undersrtand it wiothout severe cognitive thinking

It can help beginners to learn react hooks easily. The beginners can reason about their changes easily and also avoid unintended runs of hooks. Hopefully this hook can save a lot of frustation for newcomers.

To solve all the above problems, I tried to create something which can enhance developer experience. Let's see how I tried to solve the problem.

Usage with babel plugin (Recommended)

The package can also be used with a babel plugin which make it more easy to debug.

npm i @simbathesailor/use-what-changed --save-dev

npm i @simbathesailor/babel-plugin-use-what-changed --save-dev

Add the plugin entry to your babel configurations

{
  "plugins": [
    [
      "@simbathesailor/babel-plugin-use-what-changed",
      {
        "active": process.env.NODE_ENV === "development" // boolean
      }
    ]
  ]
}

Make sure the comments are enabled for your development build. As the plugin is solely dependent on the comments.

Now to debug a useEffect, useMemo or useCallback. You can do something like this:

Debug individual hooks

// uwc-debug
React.useEffect(() => {
  // console.log("some thing changed , need to figure out")
}, [a, b, c, d]);

// uwc-debug
const d = React.useCallback(() => {
  // console.log("some thing changed , need to figure out")
}, [a, b, d]);

// uwc-debug
const d = React.useMemo(() => {
  // console.log("some thing changed , need to figure out")
}, [a]);

// uwc-debug
const d = React.useLayoutEffect(() => {
  // console.log("some thing changed , need to figure out")
}, [a]);

Notice the comments uwc-debug in above examples. The comment uwc-debug is responsible for the all the magic.

Debug complete file or line below it.

Notice the comments uwc-debug-below below examples.

React.useEffect(() => {
  // console.log("some thing changed , need to figure out")
}, [a, b, c, d]);

// this comment enables tracking all the hooks below this line. so in this case useCallback and useMemo will be tracked.
// uwc-debug-below
const d = React.useCallback(() => {
  // console.log("some thing changed , need to figure out")
}, [a, b, d]);

const d = React.useMemo(() => {
  // console.log("some thing changed , need to figure out")
}, [a]);

So the example will debug all the hooks below line containing // uwc-debug-below.

No need to add any import for use-what-changed. just add a comment uwc-debug or uwc-debug-below above your hooks and you should start seeing use-what-changed debug consoles. No more back and forth across files and browser, adding debuggers and consoles.

This plugin provides following information :

1. Hook name which it is debugging.

2. File name where hook is written

3. Name of dependencies passed to hook.

4. what has changed in dependency array which caused the re-run of hook with symbol icons ( ✅, ⏺).

5. Tells you old value and new value of all the dependencies.

6. Tells you whether it is a first run or an update. I found it very helpful in debugging cases.

7. Unique color coding and id for individual hooks for easy inspection

Note: Frankly speaking the whole package was built, cause I was facing problems with hooks and debugging it was eating up a lot of my time. Definitely using this custom hook with babel plugin have saved me a lot of time and also understand unknown edge cases while using hooks

Usage without babel plugin

When only dependency are passed as the single argument

import {
  useWhatChanged,
  setUseWhatChange,
} from '@simbathesailor/use-what-changed';

// Only Once in your app you can set whether to enable hooks tracking or not.
// In CRA(create-react-app) e.g. this can be done in src/index.js

setUseWhatChange(process.env.NODE_ENV === 'development');

// This way the tracking will only happen in devlopment mode and will not
// happen in non-devlopment mode

function App() {
  const [a, setA] = React.useState(0);

  const [b, setB] = React.useState(0);

  const [c, setC] = React.useState(0);

  const [d, setD] = React.useState(0);

  // Just place the useWhatChanged hook call with dependency before your

  // useEffect, useCallback or useMemo

  useWhatChanged([a, b, c, d]); // debugs the below useEffect

  React.useEffect(() => {
    // console.log("some thing changed , need to figure out")
  }, [a, b, c, d]);

  return <div className="container">Your app jsx</div>;
}

Above snapshot show the console log when b and c has changed in the above code example.

Pass two arguments to useWhatChanged which makes it possible for useWhatChanged to log the names of the variables also.

useWhatChanged([a, b, c, d], 'a, b, c, d', 'anysuffix-string'); // debugs the below useEffect

Color coding

A unique background color will be given to each title text. It helps us in recognising the specific effect when debugging. A unique id is also given to help the debugging further.