DEV Community

Shanthi's Dev Diary
Shanthi's Dev Diary

Posted on

Understanding the <Activity> Component in React 19

#react #react19 #frontend #javascript

React 19 continues to push the boundaries of UI performance and control. One of the quieter—but powerful—additions is the <Activity> component.

At first glance, it looks like another conditional rendering helper. But under the hood, <Activity> solves a long-standing problem in React apps:

hiding UI without destroying its state or effects.

Let’s break it down.

🤔 The Problem with Conditional Rendering

In React today, hiding UI usually means unmounting it:

{isVisible && <ChatWindow />}
Enter fullscreen mode Exit fullscreen mode

When isVisible becomes false:

  • The component unmounts
  • State is lost
  • Effects are cleaned up
  • Timers, subscriptions, and caches reset

This is often not what we want.

🆕 Enter <Activity> in React 19

The <Activity> component allows you to:

  • Hide UI
  • Keep it mounted
  • Preserve state, effects, and subscriptions

Think of it as pausing visibility, not lifecycle.

✨ Basic Usage 

import { Activity } from "react";

<Activity visible={isVisible}>
  <ChatWindow />
</Activity>
Enter fullscreen mode Exit fullscreen mode

What happens here?

  • When visible={false}:
    • The UI is hidden
    • The component stays mounted
  • When visible={true}:
    • The UI reappears instantly
    • State is preserved

🧠 How <Activity> Thinks

Behavior Conditional Rendering <Activity>
Component mounted ❌ No ✅ Yes
State preserved ❌ No ✅ Yes
Effects retained ❌ No ✅ Yes
UI visible Conditional Controlled

🔥 Real-World Use Cases

1️⃣ Tabbed Interfaces

Switch tabs without losing form input or scroll position.

<Activity visible={activeTab === "profile"}>
  <ProfileForm />
</Activity>
Enter fullscreen mode Exit fullscreen mode

2️⃣ Modals & Drawers

Avoid re-initializing data every time a modal opens.

<Activity visible={isOpen}>
  <SettingsModal />
</Activity>
Enter fullscreen mode Exit fullscreen mode

3️⃣ Background UI

Keep background widgets alive but invisible.

<Activity visible={false}>
  <LiveSyncService />
</Activity>
Enter fullscreen mode Exit fullscreen mode

⚠️ Things to Keep in Mind

  • <Activity> does not stop effects
  • Background logic continues running
  • Use carefully with:
    • Polling
    • Intervals
    • Heavy subscriptions

If you want effects to pause, you must handle that explicitly.

🧩 <Activity> vs Suspense

Feature Suspense Activity
Handles async loading ✅ ❌
Controls visibility ❌ ✅
Preserves state ⚠️ Partial ✅
Lifecycle remains ❌ ✅

They solve different problems and work well together.

🧠 Mental Model

Suspense delays rendering.

Activity hides rendering.

🚀 Why This Matters

<Activity> enables:

  • Faster UI transitions
  • Better UX
  • Fewer unnecessary remounts
  • More control over component lifecycles

It’s a small API with big architectural implications.

🏁 Final Thoughts

React 19’s <Activity> component is a step toward intentional UI lifecycles—where visibility and existence are no longer the same thing.

If you’ve ever wished for:

“Hide this component, but don’t reset it”

<Activity> is your answer.

💬 Have thoughts or use cases in mind?

Drop them in the comments—let’s discuss React 19 together.

Top comments (0)