From Hooks To Actions: What's New In React 19

With the release of React 19.2, let's explore in brief how you can leverage the latest React features in your applications. Just a heads up, this blog post is more theory heavy. In case you want to see some working examples, I've linked a video in the references as well as the official documentation so that you can experiment with these features on your own time as well.

1. React Compiler

This is the one that's most exciting and anticipated by people in my opinion. React compiler is a build tool that automatically optimizes your app.

Before: review component logic and separate out states or apply memoization manually

After: configure in your bundler and see the magic

There are some caveats here however. Your app needs to follow Rules of React or the compiler will err on the safe side and choose to not apply any memoization automatically in such cases. Also, there may be unintended consequences to optimizing - there may be some bugs due to memoization that weren't there before.

So, how can you safely roll this out?

The React team recommends incremental adoption and has various configurations to support the same.

Feature flag

Dynamically control if the compiler is enabled or not; maybe you can roll it out to some user groups or segments and measure performance

//in your bundler config

gating: {

  source: 'ReactCompilerFeatureFlags', //file name

  importSpecifierName: 'isCompilerEnabled', //function name

},



// ReactCompilerFeatureFlags.js

export function isCompilerEnabled() {

  // Use your feature flag system

  return getFeatureFlag('react-compiler-enabled');

}

Opt in approach

By setting compilationMode: 'annotation', you can then opt in to compiler behaviour for necessary components with the "use memo" directive.

Opt out approach

By default, with just React Compiler enabled, you would have an opt out approach where you can specify components which are not to be processed by the compiler using "use no memo" directive

2. React performance tracks

With React 19.2, a custom set of performance tracks have been added for profiling, debugging and general monitoring in the performance tab of devtools.

Scheduler view : What is React working on?

Blocking (user interactions) / Transitions / Suspense / Idle

Components view : What components are being rendered by react in how much time?

In the comments, do let me know which feature you found most exciting or what you've tried out so far!