Optimizing Performance in React 19: Advanced Techniques and Best Practices

Optimizing performance in React applications isn’t just a best practice, it’s essential for delivering fast, smooth, and enjoyable user experiences. With the release of React 19, we now have new tools that take optimization to the next level. By combining these improvements with proven techniques, we can build much more efficient apps without adding unnecessary complexity.

Why Migrate to React 19?

React 19 represents a major leap forward in terms of performance and efficiency. The introduction of the React Compiler enables automatic optimizations that previously required manual implementation. This version is specifically designed to tackle the most common performance bottlenecks in modern applications.

React 19 with Vite or Next.js?

One of the questions I get most often when talking about React 19 is: “Which environment is better for taking advantage of it: Vite or Next.js?” Honestly, both offer excellent performance. React 19 is built to be fast and efficient regardless of the bundler or framework you choose.

Personally, I tend to use Vite for internal or administrative systems, especially in enterprise environments where SEO isn’t a priority. Vite is incredibly fast, requires minimal configuration, and lets me iterate quickly during development.

On the other hand, for public-facing projects, digital products, or websites where SEO and server-side performance are critical, Next.js remains my go-to choice. Its support for Server Components, Server Actions, and hybrid rendering makes it ideal for unlocking the full potential of React 19 in production.

React Compiler: The Optimization Revolution

This tool analyzes your code in real time and applies optimizations that used to require hooks like useMemo, useCallback, or even React.memo. What once had to be done manually and was prone to mistakes, is now automatic and much cleaner:

typescript

// Code before React 19 - Manual optimization required
const ExpensiveComponent = React.memo(({ data, onAction }) => {
  const processedData = useMemo(() => processData(data), [data])
  const handleAction = useCallback(() => onAction(processedData), [onAction, processedData])

  return  { processedData } 
})

// Code with React 19 - Automatic Optimization
const ExpensiveComponent = ({ data, onAction }) => {
  const processedData = processData(data)
  const handleAction = () => onAction(processedData)

  return  { processedData } 
}

In my projects, this has significantly simplified the code, especially in components that handle heavy logic or receive many props. The compiler automatically detects dependencies and applies smart memoization only when it truly benefits performance. It’s like having an assistant that optimizes your code for you, without needing to think twice.

Strategic Code Splitting for Efficient Loading

When building large-scale applications, loading everything at once doesn’t make sense. That’s why one of the best techniques to apply is code splitting using React.lazy and Suspense. This allows components to load only when the user actually needs them, improving initial load time and perceived performance.

In systems with multiple views or dashboards, this strategy makes a noticeable difference:

typescript

import { lazy, Suspense } from "react"

const Dashboard = lazy(() => import("./Dashboard"))
const Analytics = lazy(() => import("./Analytics"))

function App() {
  const [currentView, setCurrentView] = useState("dashboard")

  return (
    
      
        
        
      

      
         Loading...  }>
          {currentView === "dashboard" ?  : }

)
}

List Optimization with Proper Keys

When working with lists, using the correct key is more important than it seems. A well-defined key helps React identify which elements have changed, been added, or removed, preventing unnecessary re-renders and improving performance.

Whenever possible, I use unique and stable IDs like user.id. I avoid using the array index as a key, because even if it appears to work, it can cause issues when the list changes dynamically. This is one of those simple practices that makes a big impact in applications with frequent updates:

typescript

// ✅ Correct use of keys - unique and stable IDs
function UserList({ users }) {
  return users.map(user => (
    
  ))
}

// ❌ Incorrect use of keys - index as key
function BadUserList({ users }) {
  return users.map((user, index) => (
    
  ))
}

List Virtualization for Scalable Interfaces

A lesser-known but highly effective technique in specific scenarios is list virtualization. When an interface needs to render hundreds or thousands of elements, like in infinite scroll or large data tables, performance can suffer if everything is mounted in the DOM at once.

Virtualization solves this by rendering only the items visible on screen, keeping off-screen elements out of the DOM. This reduces memory usage, improves scroll performance, and prevents unnecessary blocking.

There are several libraries that implement this technique, such as react-window, react-virtualized, or @tanstack/virtual. For this example, I’ll use react-window, which is lightweight and easy to integrate:

typescript

import { FixedSizeList as List } from "react-window"

const users = [...Array(5000)].map((_, i) => ({ id: i, name: `Usuario ${i}` }))

function VirtualizedUserList() {
  return (
    
      {({ index, style }) => (
        
          {users[index].name}
        
      )}
    
  )
}

This technique is especially useful in interfaces with infinite scroll, where data accumulates on the client and the number of elements grows with each interaction. In those cases, virtualization can make a significant difference in user experience.

Virtualization or Pagination?

Both are valid techniques for improving performance in large lists, but they’re not always used together. Pagination limits the amount of data fetched from the server, while virtualization optimizes how that data is rendered on the client.

In most of my projects, I prefer to have data paginated from the server, as it reduces the weight of each request and avoids loading unnecessary information. Virtualization makes more sense when the backend delivers large datasets all at once, or when implementing infinite scroll without clearing previous data.

Avoid Inline and Anonymous Functions in JSX

Another detail I pay close attention to is avoiding inline functions inside JSX. While they may seem harmless, each time the component re-renders, a new reference to that function is created. This can trigger unnecessary re-renders in child components.

The solution is to separate logic into stable functions or dedicated components. In my experience, this not only improves performance but also makes the code cleaner and easier to maintain:

typescript

// ❌ Avoid - inline function
function TodoList({ todos, onDelete }): React.JSX.Element {
  return (
    
      {todos.map(todo => (
         onDelete(todo.id)} // New function each render
        />
      ))}
    
  )
}

// ✅ Better approach - separate component
function TodoList({ todos, onDelete }): React.JSX.Element {
  return (
    
      {todos.map(todo => (
        
      ))}
    
  )
}

// TodoItem component
function TodoItem ({ todo, onDelete }): React.JSX.Element {
  const handleDelete = () => onDelete(todo.id)

  return (
    
      {todo.text}
      
    
  )
}

Enhanced Server-Side Rendering (SSR)

One of the most powerful improvements in React 19 is its ability to stream content from the server, combining Suspense with progressive loading. This allows parts of the interface to render while others are still loading, improving perceived speed and reducing wait times for users.

That said, this type of rendering, especially when using use() and components that consume promises directly, is only available natively in Next.js. If you're using Vite or another environment without support for React Server Components, these techniques won’t work as expected:

typescript

// Server-side component with streaming
async function ProductPage({ productId }) {
  const product = await fetchProduct(productId)
  const reviews = fetchReviews(productId) // No await - streaming

  return (
    
      
      }>
        
      
    
  )
}

// Client-side component that consumes the promise
function Reviews({ reviewsPromise }): React.JSX.Element {
  const reviews = use(reviewsPromise)

  return reviews.map(review => (
    
  ))
}

Actions for Efficient State Management

Instead of relying on useState or useReducer to handle forms and async requests, React 19 introduces a new way to define server-side functions that integrate directly into the component flow.

What’s interesting is that these actions run on the server, while React handles the state, transitions, and user feedback automatically. However, and this is important, this functionality is also exclusive to environments like Next.js, which support React Server Components and recognize the "use server" directive:

typescript

// Server Action with state management
async function updateUser(prevState, formData) {
  "use server"

  try {
    const updates = Object.fromEntries(formData)
    await saveUserUpdates(updates)
    return { success: true, message: "User updated" }
  } catch (error) {
    return { success: false, message: "Error updating user" }
  }
}

// Usage in component
function UserForm({ user }) {
  const [state, formAction, isPending] = useActionState(updateUser, null)

  return (
    
      
      
      
      {state?.message && {state.message} }
    
  )
}

Conclusion and Next Steps

React 19 marks a turning point in how we approach performance in our applications. The combination of the new compiler with proven optimization techniques allows us to build faster, cleaner, and more efficient interfaces, without the need for manual tweaks.

If you're ready to take the leap, here’s what I recommend:

Update your dependencies to the latest versions of React and related tools

Migrate components gradually, taking advantage of new features without breaking existing functionality

Monitor performance using tools like Lighthouse, Web Vitals, or your preferred solution

Experiment with Server Components and Actions in new projects, especially if you're using Next.js

Performance optimization isn’t a destination, it’s an ongoing process. React 19 gives us powerful tools, but it’s still up to us as developers to apply them wisely, based on the context and needs of each project.

Optimizing Performance in React 19: Advanced Techniques and Best Practices