How do animations work in React Native?

Question

IT Interview Practice · Accepted Answer

React Native supports **animations** through the built-in **Animated** API and the popular **Reanimated** library. Animations enhance UX with smooth motion and transitions. Performance (running animations on the native thread) is a key consideration. ## The Animated API (built-in) ```jsx import { Animated } from 'react-native'; const fadeAnim = useRef(new Animated.Value(0)).current; // an animated value // animate it (e.g. fade in) Animated.timing(fadeAnim, { toValue: 1, duration: 500, useNativeDriver: true, // run on the NATIVE thread (smooth — important!) }).start(); // apply it to a component ... ``` The **Animated** API uses animated values applied to `Animated.View` etc. The crucial `useNativeDriver: true` runs the animation on the **native thread** (smooth, not blocked by JS). ## Reanimated (recommended for complex animations) ```text REACT NATIVE REANIMATED → a popular library for performant, complex animations: → runs animations on the native/UI thread (smooth, off the JS thread) → supports gestures (with react-native-gesture-handler), worklets, spring physics → better for complex, interactive, gesture-driven animations than the basic Animated API → The go-to for advanced animations in React Native. ``` ## Why performance matters here ```text ⚠️ Animations driven by the JS thread can be JANKY (the JS thread is busy / blocked) → → useNativeDriver (Animated) or Reanimated run animations on the NATIVE/UI thread → smooth even if JS is busy → Running animations natively (not on the JS thread) is KEY to smooth animations in RN. ``` ## Why it matters Understanding animations in React Native is valuable because **animations enhance user experience** with smooth motion and transitions that make apps feel polished, so it's useful practical knowledge — and the performance considerations are particularly important in React Native. The built-in **Animated** API (using animated values applied to Animated components) provides the foundation for animations. Critically, understanding the performance aspect — that **animations driven by the JavaScript thread can be janky** (if the JS thread is busy) and that running animations on the **native/UI thread** (via `useNativeDriver: true` in Animated, or via Reanimated) keeps them smooth even when JS is busy — is the key insight for performant animations in React Native, a notable consideration given React Native's JS/native threading model. Understanding **Reanimated** (the popular library for performant, complex, gesture-driven animations that runs on the native thread, supporting worklets, spring physics, and gestures) is valuable because it's the **go-to for advanced animations** in React Native, better than the basic Animated API for complex interactive animations. Understanding both — the built-in Animated API (with useNativeDriver) for simpler animations and Reanimated for complex ones, both emphasizing running animations natively for smoothness — covers the animation toolkit. Polished animations meaningfully improve UX, and getting them smooth (by running on the native thread) is the key challenge React Native's architecture presents. Since smooth animations enhance UX and React Native's animation performance depends critically on running animations on the native thread (via useNativeDriver or Reanimated), and since understanding the Animated API, Reanimated, and especially the native-thread performance consideration enables building smooth animations, understanding animations in React Native is valuable, practically-relevant knowledge — useful for enhancing UX with motion, where the React-Native-specific concern of running animations natively for smoothness is particularly important, a valuable skill for building polished React Native apps.

The Animated API (built-in)

Reanimated (recommended for complex animations)

Why performance matters here

Why it matters

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