react-performance-coach

A little library to help you write more performant React apps.

It provides a hook usePerformanceCoach that causes your component to re-render itself every 1 second. Once you do this, you can use React Developer Tools to see which components are re-rendering needlessly. You can then use this information to optimize your app.

Generally, it is fine to re-render a few top-level components every second — if it doesn’t lead to a snowball effect where a top-level component causes the entire subtree to re-render itself.

How to use

Install the react-performance-coach package and install React Developer Tools in your browser.
```
yarn add react-performance-coach
```

In your main app component, use the usePerformanceCoach hook.

import { usePerformanceCoach } from 'react-performance-coach'

export default function App() {
  usePerformanceCoach()
  // ...
}

In the page component that you want to optimize, use the usePerformanceCoach hook.

import { usePerformanceCoach } from 'react-performance-coach'

export default function ChatPage() {
  usePerformanceCoach()
  // ...
}

Run your app in a development server.
Open React Developer Tools and make sure that Highlight updates when components render is enabled.
Every second, the components that has performance coach installed will re-render. There will be a flashing box around the component that re-rendered.

Ideally, when you see a flashing box around a component, something in that box should have changed. If nothing has changed, then you know that the component is re-rendering needlessly.

Generally, it is fine to have a few components that re-render needlessly. But if you have hundreds of consistently flashing boxes, then that would indicate that you have a performance problem.
Use the above information to optimize your app. For example, if you see a flashing box around a component that renders a list of items, then you can use React.memo to prevent the component from re-rendering when the list of items does not change.

Once optimized, there should be a smaller number of flashing boxes.