How to use Profiler API in React to measure render performance

To use Profiler API in React to measure render performance, you can follow the below steps.

1. Import the Profiler component for react.
2. Wrap the components you want to measure render time with the Profiler component.
3. Define the callback function.
4. Run the application and check the console output.

The React Profiler API is a tool that can help to find performance problems in our React application. This will track the rendering time of each component and help us to identify which components are causing performance bottlenecks.

Let us explain how to use the React Profiler API in React to measure render performance with an example.

Say you have a React application with the component hierarchy below.

<App>
  	<Header />
  	<Main>
    	<Sidebar />
    	<Content />
  	</Main>
  	<Footer />
</App>

If you think some of the components take too much time to render and are causing performance issues, you can use the Profiler API to track their rendering times. Let us explain all the steps to measure render performance in detail.

Import the Profiler component

First, import the Profiler component from React:

import React, { Profiler } from 'react';

Wrap the components with the Profiler component

Wrap each of the components that you want to profile with the Profiler component and pass it a callback function:

function App() {
  return (
    <div>
      	<Profiler id="Header" onRender={callback}>
        	<Header />
      	</Profiler>
      	<Main>
        	<Profiler id="Sidebar" onRender={callback}>
          		<Sidebar />
        	</Profiler>
        	<Profiler id="Content" onRender={callback}>
          		<Content />
        	</Profiler>
      	</Main>
      	<Profiler id="Footer" onRender={callback}>
        	<Footer />
      	</Profiler>
    </div>
  );
}

In this example, we're profiling the Header, Sidebar, Content, and Footer components. So we wrapped them with the Profiler component.

Define the callback function

The next step is to define the callback function.

function callback(
  id,
  phase,
  actualDuration,
  baseDuration,
  startTime,
  commitTime
) {
  console.log(`${id} took ${actualDuration}ms to render.`);
}

In this example, we're just writing to the console the name of the component and how long it took to render.

An overview of the arguments sent to the callback function is given below:

1. id: This is a string that identifies the component being profiled. This can be used to distinguish between various components that are being profiled simultaneously.
2. phase: This is a string that indicates whether the component is being mounted for the first time ("mount") or updated due to a change in the state or prop("update").
3. actualDuration: This is the time that took in milliseconds for rendering the committed update
4. baseDuration: This is an estimated time taken to render the component and its entire subtree without memoization
5. startTime: This is a timestamp of when the rendering process started.
6. commitTime: This is a timestamp of when the rendering process was completed and the DOM updates were made.

Run the application and check the console output

Next, run the react application. When you run the react application, the Profiler API will log the rendering time of each component into the console. Here is a sample console output.

Header took 4.987ms to render.
Sidebar took 157.123ms to render.
Content took 35.456ms to render.
Footer took 2.345ms to render.

In this example, we can see that the Sidebar component is taking more time to render than the other components. So Sidebar component may be causing a performance issue for the App component. Then we can investigate the Sidebar component further to identify and address the performance issues.

By using the React Profiler API, we can get insights into the rendering times of individual components and identify performance issues more easily. This will help us to optimize our applications to provide a better user experience.

The React Profiler API is only available in React versions greater than 16.5. If you are using an older version of React, you are not able to use the Profiler API.

When you build your application for production, the Profiler component should be removed from the production build to reduce the overhead of profiling.

Conclusion

To use Profiler API in React to measure render performance, import the Profiler component from React and wrap the component that you want to measure render time with the Profiler component. Then define the onRender callback function that will receive parameters to measure the component's rendering time and take any necessary optimization steps based on the results.