Media & Animation Events

Q: How do I detect when a video is buffering?

Use onWaiting to detect when playback stalls due to insufficient data Use onSeeked or onCanPlay to detect when enough data is available to resume Show a loading spinner between onWaiting and the next onSeeked/onCanPlay

Q: How do I chain multiple CSS animations on the same element?

Listen to onAnimationEnd and change the CSS class to trigger the next animation Check e.animationName to know which animation just finished Set state to apply the next animation class, creating a sequential chain

Q: How do I build a custom progress bar for a video player?

Use onLoadedData to get video.duration Use onTimeUpdate to track video.currentTime Calculate (currentTime / duration) * 100 for the progress percentage For smoother updates, use requestAnimationFrame instead of onTimeUpdate

Q: Can I detect when a CSS animation loops with onAnimationIteration?

Yes, onAnimationIteration fires at the end of each iteration for animations with animation-iteration-count greater than 1 It does not fire at the end of the last iteration -- use onAnimationEnd for that The event includes animationName and elapsedTime to identify which cycle completed

Handle video/audio playback state changes, image loading, CSS transitions, and animation lifecycle events.

Event Reference

Media Events (Video & Audio)

Event	Fires When	Event Object
`onPlay`	Playback starts or resumes	`React.SyntheticEvent`
`onPause`	Playback is paused	`React.SyntheticEvent`
`onEnded`	Playback reaches the end	`React.SyntheticEvent`
`onTimeUpdate`	The current playback time changes (fires frequently)	`React.SyntheticEvent`
`onVolumeChange`	Volume or mute state changes	`React.SyntheticEvent`
`onLoadedData`	The first frame of media has loaded	`React.SyntheticEvent`
`onError`	Media loading fails	`React.SyntheticEvent`
`onWaiting`	Playback stalls due to buffering	`React.SyntheticEvent`
`onSeeking`	A seek operation begins	`React.SyntheticEvent`
`onSeeked`	A seek operation completes	`React.SyntheticEvent`

Image Events

Event	Fires When	Event Object
`onLoad`	The image finishes loading	`React.SyntheticEvent`
`onError`	The image fails to load	`React.SyntheticEvent`

CSS Animation Events

Event	Fires When	Event Object
`onAnimationStart`	A CSS animation begins	`React.AnimationEvent`
`onAnimationEnd`	A CSS animation completes	`React.AnimationEvent`
`onAnimationIteration`	A CSS animation loop restarts	`React.AnimationEvent`

CSS Transition Events

Event	Fires When	Event Object
`onTransitionEnd`	A CSS transition completes	`React.TransitionEvent`

Recipe

Quick-reference recipe card -- copy-paste ready.

// Video play/pause
"use client";
 
import { useRef, useState } from "react";
 
export function VideoToggle({ src }: { src: string }) {
  const videoRef = useRef<HTMLVideoElement>(null);
  const [playing, setPlaying] = useState(false);
 
  const toggle = () => {
    if (videoRef.current?.paused) {
      videoRef.current.play();
    } else {
      videoRef.current?.pause();
    }
  };
 
  return (
    <div>
      <video
        ref={videoRef}
        src={src}
        onPlay={() => setPlaying(true)}
        onPause={() => setPlaying(false)}
      />
      <button onClick={toggle}>{playing ? "Pause" : "Play"}</button>
    </div>
  );
}

// Image onLoad / onError
"use client";
 
import { useState } from "react";
 
export function SafeImage({ src, alt }: { src: string; alt: string }) {
  const [loaded, setLoaded] = useState(false);
  const [error, setError] = useState(false);
 
  if (error) return <div className="bg-gray-200 p-4">Failed to load image</div>;
 
  return (
    <img
      src={src}
      alt={alt}
      onLoad={() => setLoaded(true)}
      onError={() => setError(true)}
      className={loaded ? "opacity-100" : "opacity-0"}
      style={{ transition: "opacity 0.3s" }}
    />
  );
}

// Animation end callback
"use client";
 
import { useState } from "react";
 
export function FadeOutAndRemove() {
  const [visible, setVisible] = useState(true);
  const [animating, setAnimating] = useState(false);
 
  const handleDismiss = () => setAnimating(true);
 
  if (!visible) return null;
 
  return (
    <div
      className={animating ? "animate-fadeOut" : ""}
      onAnimationEnd={() => {
        if (animating) setVisible(false);
      }}
    >
      <p>I will fade away</p>
      <button onClick={handleDismiss}>Dismiss</button>
    </div>
  );
}

When to reach for this: You need to synchronize UI state with media playback, image loading lifecycle, or CSS animation/transition completion.

Working Example

// CustomVideoPlayer.tsx
"use client";
 
import { useRef, useState, useCallback } from "react";
 
export default function CustomVideoPlayer({ src }: { src: string }) {
  const videoRef = useRef<HTMLVideoElement>(null);
  const [playing, setPlaying] = useState(false);
  const [currentTime, setCurrentTime] = useState(0);
  const [duration, setDuration] = useState(0);
  const [volume, setVolume] = useState(1);
  const [muted, setMuted] = useState(false);
  const [buffering, setBuffering] = useState(false);
 
  const togglePlay = useCallback(() => {
    const video = videoRef.current;
    if (!video) return;
    if (video.paused) {
      video.play();
    } else {
      video.pause();
    }
  }, []);
 
  const handleTimeUpdate = useCallback(
    (e: React.SyntheticEvent<HTMLVideoElement>) => {
      setCurrentTime(e.currentTarget.currentTime);
    },
    []
  );
 
  const handleLoadedData = useCallback(
    (e: React.SyntheticEvent<HTMLVideoElement>) => {
      setDuration(e.currentTarget.duration);
    },
    []
  );
 
  const handleVolumeChange = useCallback(
    (e: React.SyntheticEvent<HTMLVideoElement>) => {
      setVolume(e.currentTarget.volume);
      setMuted(e.currentTarget.muted);
    },
    []
  );
 
  const handleSeek = useCallback(
    (e: React.ChangeEvent<HTMLInputElement>) => {
      const video = videoRef.current;
      if (!video) return;
      video.currentTime = Number(e.target.value);
    },
    []
  );
 
  const handleVolumeSlider = useCallback(
    (e: React.ChangeEvent<HTMLInputElement>) => {
      const video = videoRef.current;
      if (!video) return;
      video.volume = Number(e.target.value);
    },
    []
  );
 
  const toggleMute = useCallback(() => {
    const video = videoRef.current;
    if (!video) return;
    video.muted = !video.muted;
  }, []);
 
  const formatTime = (seconds: number) => {
    const m = Math.floor(seconds / 60);
    const s = Math.floor(seconds % 60);
    return `${m}:${s.toString().padStart(2, "0")}`;
  };
 
  const progress = duration > 0 ? (currentTime / duration) * 100 : 0;
 
  return (
    <div className="max-w-2xl mx-auto bg-black rounded-xl overflow-hidden">
      <div className="relative">
        <video
          ref={videoRef}
          src={src}
          className="w-full"
          onPlay={() => setPlaying(true)}
          onPause={() => setPlaying(false)}
          onTimeUpdate={handleTimeUpdate}
          onLoadedData={handleLoadedData}
          onVolumeChange={handleVolumeChange}
          onWaiting={() => setBuffering(true)}
          onSeeked={() => setBuffering(false)}
          onEnded={() => setPlaying(false)}
          onClick={togglePlay}
        />
 
        {buffering && (
          <div className="absolute inset-0 flex items-center justify-center bg-black/30">
            <div className="w-10 h-10 border-4 border-white border-t-transparent rounded-full animate-spin" />
          </div>
        )}
      </div>
 
      {/* Progress bar */}
      <div className="px-4 pt-2">
        <div className="relative h-1 bg-gray-700 rounded-full">
          <div
            className="absolute h-full bg-blue-500 rounded-full"
            style={{ width: `${progress}%` }}
          />
        </div>
        <input
          type="range"
          min={0}
          max={duration || 0}
          step={0.1}
          value={currentTime}
          onChange={handleSeek}
          className="w-full opacity-0 absolute cursor-pointer"
          style={{ marginTop: "-6px", height: "12px" }}
          aria-label="Seek"
        />
      </div>
 
      {/* Controls */}
      <div className="flex items-center gap-4 p-4 text-white">
        <button
          onClick={togglePlay}
          className="text-xl"
          aria-label={playing ? "Pause" : "Play"}
        >
          {playing ? "⏸" : "▶"}
        </button>
 
        <span className="text-sm font-mono">
          {formatTime(currentTime)} / {formatTime(duration)}
        </span>
 
        <div className="flex items-center gap-2 ml-auto">
          <button onClick={toggleMute} aria-label={muted ? "Unmute" : "Mute"}>
            {muted || volume === 0 ? "🔇" : "🔊"}
          </button>
          <input
            type="range"
            min={0}
            max={1}
            step={0.05}
            value={muted ? 0 : volume}
            onChange={handleVolumeSlider}
            className="w-20"
            aria-label="Volume"
          />
        </div>
      </div>
    </div>
  );
}

What this demonstrates:

Using onPlay, onPause, and onEnded to track playback state
Using onTimeUpdate to sync a progress bar with the current time
Using onLoadedData to capture the video duration
Using onVolumeChange to reflect volume and mute state changes
Using onWaiting and onSeeked for buffering indicator
Controlling the video element via ref while listening to events for state sync

Deep Dive

How It Works

Media events are dispatched by the browser's native <video> and <audio> elements. React wraps them as SyntheticEvent instances.
onTimeUpdate fires approximately 4 times per second during playback (browser-dependent, not tied to requestAnimationFrame).
Image onLoad fires after the image is fully decoded and ready to display. onError fires if the source URL fails.
CSS onAnimationEnd fires once per animation per element. If multiple animations run on the same element, it fires for each.
onTransitionEnd fires for each CSS property that transitions. Transitioning all properties may produce multiple events.

Variations

Image lazy loading with fade-in on load:

"use client";
 
import { useState, useCallback } from "react";
 
export function LazyImage({
  src,
  alt,
  width,
  height,
}: {
  src: string;
  alt: string;
  width: number;
  height: number;
}) {
  const [loaded, setLoaded] = useState(false);
  const [error, setError] = useState(false);
 
  const handleLoad = useCallback(() => setLoaded(true), []);
  const handleError = useCallback(() => setError(true), []);
 
  return (
    <div
      className="relative overflow-hidden bg-gray-100"
      style={{ width, height }}
    >
      {error ? (
        <div className="flex items-center justify-center w-full h-full text-gray-400">
          Failed to load
        </div>
      ) : (
        <>
          {!loaded && (
            <div className="absolute inset-0 animate-pulse bg-gray-200" />
          )}
          <img
            src={src}
            alt={alt}
            loading="lazy"
            onLoad={handleLoad}
            onError={handleError}
            className={`w-full h-full object-cover transition-opacity duration-500 ${
              loaded ? "opacity-100" : "opacity-0"
            }`}
          />
        </>
      )}
    </div>
  );
}

Animation chaining with onAnimationEnd:

"use client";
 
import { useState, useCallback } from "react";
 
type Phase = "idle" | "slideIn" | "pulse" | "slideOut" | "done";
 
export function AnimationChain() {
  const [phase, setPhase] = useState<Phase>("idle");
 
  const start = useCallback(() => setPhase("slideIn"), []);
 
  const handleAnimationEnd = useCallback(
    (e: React.AnimationEvent) => {
      // Only handle animations on this specific element
      if (e.target !== e.currentTarget) return;
 
      const transitions: Record<string, Phase> = {
        slideIn: "pulse",
        pulse: "slideOut",
        slideOut: "done",
      };
      const next = transitions[phase];
      if (next) setPhase(next);
    },
    [phase]
  );
 
  if (phase === "done") {
    return <button onClick={() => setPhase("idle")}>Reset</button>;
  }
 
  const animationClass: Record<Phase, string> = {
    idle: "",
    slideIn: "animate-slideInRight",
    pulse: "animate-pulse",
    slideOut: "animate-slideOutLeft",
    done: "",
  };
 
  return (
    <div>
      {phase === "idle" ? (
        <button onClick={start}>Start Animation Chain</button>
      ) : (
        <div
          className={`p-8 bg-blue-500 text-white rounded-lg ${animationClass[phase]}`}
          onAnimationEnd={handleAnimationEnd}
        >
          Phase: {phase}
        </div>
      )}
    </div>
  );
}

Transition completion callback:

"use client";
 
import { useState, useCallback } from "react";
 
export function CollapsePanel({
  children,
  title,
}: {
  children: React.ReactNode;
  title: string;
}) {
  const [open, setOpen] = useState(false);
  const [rendered, setRendered] = useState(false);
 
  const toggle = useCallback(() => {
    if (!open) {
      setRendered(true); // mount content before expanding
      requestAnimationFrame(() => setOpen(true));
    } else {
      setOpen(false);
    }
  }, [open]);
 
  const handleTransitionEnd = useCallback(
    (e: React.TransitionEvent) => {
      // Only respond to height transition, not other properties
      if (e.propertyName === "max-height" && !open) {
        setRendered(false); // unmount after collapse completes
      }
    },
    [open]
  );
 
  return (
    <div className="border rounded-lg">
      <button onClick={toggle} className="w-full p-4 text-left font-semibold">
        {title} {open ? "▲" : "▼"}
      </button>
      <div
        className="overflow-hidden transition-[max-height] duration-300 ease-in-out"
        style={{ maxHeight: open ? "500px" : "0px" }}
        onTransitionEnd={handleTransitionEnd}
      >
        {rendered && <div className="p-4 border-t">{children}</div>}
      </div>
    </div>
  );
}

Audio visualization basics:

"use client";
 
import { useRef, useCallback, useEffect, useState } from "react";
 
export function AudioVisualizer({ src }: { src: string }) {
  const audioRef = useRef<HTMLAudioElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);
  const analyserRef = useRef<AnalyserNode | null>(null);
  const [initialized, setInitialized] = useState(false);
 
  const initAudio = useCallback(() => {
    if (initialized || !audioRef.current) return;
    const ctx = new AudioContext();
    const source = ctx.createMediaElementSource(audioRef.current);
    const analyser = ctx.createAnalyser();
    analyser.fftSize = 256;
    source.connect(analyser);
    analyser.connect(ctx.destination);
    analyserRef.current = analyser;
    setInitialized(true);
  }, [initialized]);
 
  useEffect(() => {
    if (!initialized) return;
    const analyser = analyserRef.current;
    const canvas = canvasRef.current;
    if (!analyser || !canvas) return;
 
    const ctx = canvas.getContext("2d");
    if (!ctx) return;
 
    const bufferLength = analyser.frequencyBinCount;
    const dataArray = new Uint8Array(bufferLength);
 
    let animationId: number;
    const draw = () => {
      animationId = requestAnimationFrame(draw);
      analyser.getByteFrequencyData(dataArray);
 
      ctx.fillStyle = "#000";
      ctx.fillRect(0, 0, canvas.width, canvas.height);
 
      const barWidth = (canvas.width / bufferLength) * 2.5;
      let x = 0;
      for (let i = 0; i < bufferLength; i++) {
        const barHeight = (dataArray[i] / 255) * canvas.height;
        ctx.fillStyle = `hsl(${(i / bufferLength) * 360}, 80%, 50%)`;
        ctx.fillRect(x, canvas.height - barHeight, barWidth, barHeight);
        x += barWidth + 1;
      }
    };
    draw();
 
    return () => cancelAnimationFrame(animationId);
  }, [initialized]);
 
  return (
    <div className="space-y-4">
      <canvas ref={canvasRef} width={600} height={200} className="bg-black rounded-lg" />
      <audio
        ref={audioRef}
        src={src}
        controls
        onPlay={initAudio}
        crossOrigin="anonymous"
      />
    </div>
  );
}

Video progress bar with preview:

"use client";
 
import { useRef, useState, useCallback } from "react";
 
export function VideoProgressBar({
  videoRef,
  duration,
  currentTime,
}: {
  videoRef: React.RefObject<HTMLVideoElement | null>;
  duration: number;
  currentTime: number;
}) {
  const barRef = useRef<HTMLDivElement>(null);
  const [hoverTime, setHoverTime] = useState<number | null>(null);
 
  const handleClick = useCallback(
    (e: React.MouseEvent<HTMLDivElement>) => {
      const rect = e.currentTarget.getBoundingClientRect();
      const fraction = (e.clientX - rect.left) / rect.width;
      if (videoRef.current) {
        videoRef.current.currentTime = fraction * duration;
      }
    },
    [videoRef, duration]
  );
 
  const handleMouseMove = useCallback(
    (e: React.MouseEvent<HTMLDivElement>) => {
      const rect = e.currentTarget.getBoundingClientRect();
      const fraction = (e.clientX - rect.left) / rect.width;
      setHoverTime(fraction * duration);
    },
    [duration]
  );
 
  const progress = duration > 0 ? (currentTime / duration) * 100 : 0;
 
  const formatTime = (s: number) =>
    `${Math.floor(s / 60)}:${Math.floor(s % 60)
      .toString()
      .padStart(2, "0")}`;
 
  return (
    <div
      ref={barRef}
      className="relative h-2 bg-gray-700 rounded cursor-pointer group"
      onClick={handleClick}
      onMouseMove={handleMouseMove}
      onMouseLeave={() => setHoverTime(null)}
    >
      <div
        className="h-full bg-blue-500 rounded"
        style={{ width: `${progress}%` }}
      />
      {hoverTime !== null && (
        <div
          className="absolute -top-8 bg-black text-white text-xs px-2 py-1 rounded -translate-x-1/2"
          style={{ left: `${(hoverTime / duration) * 100}%` }}
        >
          {formatTime(hoverTime)}
        </div>
      )}
    </div>
  );
}

TypeScript Notes

// Media event -- typed to the specific element
function handlePlay(e: React.SyntheticEvent<HTMLVideoElement>) {
  const video: HTMLVideoElement = e.currentTarget;
  const time: number = video.currentTime;
  const dur: number = video.duration;
  const paused: boolean = video.paused;
  const vol: number = video.volume;
}
 
// Audio element events use the same type
function handleAudioEnd(e: React.SyntheticEvent<HTMLAudioElement>) {
  const audio: HTMLAudioElement = e.currentTarget;
  console.log("Audio ended at", audio.duration);
}
 
// Image load/error
function handleImgLoad(e: React.SyntheticEvent<HTMLImageElement>) {
  const img: HTMLImageElement = e.currentTarget;
  const naturalWidth: number = img.naturalWidth;
  const naturalHeight: number = img.naturalHeight;
}
 
// Animation events
function handleAnimEnd(e: React.AnimationEvent<HTMLDivElement>) {
  const name: string = e.animationName; // CSS animation name
  const elapsed: number = e.elapsedTime; // seconds
  const pseudo: string = e.pseudoElement; // "::before", "::after", or ""
}
 
// Transition events
function handleTransEnd(e: React.TransitionEvent<HTMLDivElement>) {
  const property: string = e.propertyName; // e.g., "opacity", "transform"
  const elapsed: number = e.elapsedTime; // seconds
  const pseudo: string = e.pseudoElement;
}
 
// Ref typing for media elements
const videoRef = useRef<HTMLVideoElement>(null);
const audioRef = useRef<HTMLAudioElement>(null);

Gotchas

onTransitionEnd fires once per property -- Transitioning all or multiple properties (e.g., opacity and transform) fires the event multiple times. Fix: Check e.propertyName to respond only to the property you care about: if (e.propertyName !== "opacity") return;.
onAnimationEnd bubbles from child elements -- If a child has its own CSS animation, the event bubbles up to your handler. Fix: Compare e.target === e.currentTarget to ensure you only respond to your element's animation.
onTimeUpdate does not fire every frame -- It fires roughly 4 times per second, not 60. This makes it too coarse for frame-accurate UI. Fix: For smooth progress bars, use requestAnimationFrame with videoRef.current.currentTime instead.
Media onError gives minimal information -- The SyntheticEvent does not include an error code directly. Fix: Access e.currentTarget.error (a MediaError object) with e.currentTarget.error?.code and e.currentTarget.error?.message for details.
onLoad on <img> fires on cached images too -- But the timing is different: cached images may fire onLoad synchronously during render. Fix: Always initialize your loading state to false and let onLoad set it to true, rather than assuming async timing.
CSS animations on unmounted elements do not fire onAnimationEnd -- If you remove the element from the DOM before the animation finishes, the event never fires. Fix: Wait for onAnimationEnd before setting the state that removes the element, or use the Web Animations API for promise-based control.
play() returns a Promise that can reject -- Calling videoRef.current.play() returns a Promise. If the user has not interacted with the page, autoplay policies reject it. Fix: Always await or .catch() the play promise: videoRef.current.play().catch(() => { /* handle autoplay block */ }).

Alternatives

Alternative	Use When	Don't Use When
Web Animations API (`element.animate()`)	You need JS-driven animations with promises and playback control	CSS keyframes are sufficient
Framer Motion (`motion.div`)	You want declarative React animations with enter/exit/layout	You only need to handle native media events
`requestAnimationFrame`	You need frame-accurate progress tracking for video	`onTimeUpdate` precision is acceptable
`<video>` with HLS.js / dash.js	You need adaptive streaming (ABR)	A single MP4 file works fine
Next.js `<Image>`	You want automatic optimization, lazy loading, and blur placeholder	You need fine-grained `onLoad` / `onError` control with custom logic

FAQs

How do I detect when a video is buffering?

Use onWaiting to detect when playback stalls due to insufficient data
Use onSeeked or onCanPlay to detect when enough data is available to resume
Show a loading spinner between onWaiting and the next onSeeked/onCanPlay

Why does video.play() sometimes throw an error?

Browser autoplay policies require user interaction before media can play with sound
play() returns a Promise that rejects if autoplay is blocked
Always handle the rejection: video.play().catch(() => { /* show play button */ })
Videos with muted attribute are usually allowed to autoplay

How do I chain multiple CSS animations on the same element?

Listen to onAnimationEnd and change the CSS class to trigger the next animation
Check e.animationName to know which animation just finished
Set state to apply the next animation class, creating a sequential chain

Why does onTransitionEnd fire multiple times?

It fires once per CSS property that transitions
If you transition transform and opacity, you get two events
Filter by e.propertyName to respond only to the one you care about

How do I build a custom progress bar for a video player?

Use onLoadedData to get video.duration
Use onTimeUpdate to track video.currentTime
Calculate (currentTime / duration) * 100 for the progress percentage
For smoother updates, use requestAnimationFrame instead of onTimeUpdate

How do I handle image loading errors gracefully?

const [error, setError] = useState(false);
 
return error ? (
  <div className="placeholder">Image unavailable</div>
) : (
  <img
    src={src}
    alt={alt}
    onError={() => setError(true)}
  />
);

Can I detect when a CSS animation loops with onAnimationIteration?

Yes, onAnimationIteration fires at the end of each iteration for animations with animation-iteration-count greater than 1
It does not fire at the end of the last iteration -- use onAnimationEnd for that
The event includes animationName and elapsedTime to identify which cycle completed

Pointer Events -- Unified input across mouse, touch, and pen
Touch Events -- Multi-touch gesture handling for mobile
Scroll Events -- Scroll position tracking and infinite scroll

Event Reference

Media Events (Video & Audio)

Event	Fires When	Event Object
`onPlay`	Playback starts or resumes	`React.SyntheticEvent`
`onPause`	Playback is paused	`React.SyntheticEvent`
`onEnded`	Playback reaches the end	`React.SyntheticEvent`
`onTimeUpdate`	The current playback time changes (fires frequently)	`React.SyntheticEvent`
`onVolumeChange`	Volume or mute state changes	`React.SyntheticEvent`
`onLoadedData`	The first frame of media has loaded	`React.SyntheticEvent`
`onError`	Media loading fails	`React.SyntheticEvent`
`onWaiting`	Playback stalls due to buffering	`React.SyntheticEvent`
`onSeeking`	A seek operation begins	`React.SyntheticEvent`
`onSeeked`	A seek operation completes	`React.SyntheticEvent`

Image Events

Event	Fires When	Event Object
`onLoad`	The image finishes loading	`React.SyntheticEvent`
`onError`	The image fails to load	`React.SyntheticEvent`

CSS Animation Events

Event	Fires When	Event Object
`onAnimationStart`	A CSS animation begins	`React.AnimationEvent`
`onAnimationEnd`	A CSS animation completes	`React.AnimationEvent`
`onAnimationIteration`	A CSS animation loop restarts	`React.AnimationEvent`

CSS Transition Events

Event	Fires When	Event Object
`onTransitionEnd`	A CSS transition completes	`React.TransitionEvent`

Recipe

Quick-reference recipe card -- copy-paste ready.

// Video play/pause
"use client";
 
import { useRef, useState } from "react";
 
export function VideoToggle({ src }: { src: string }) {
  const videoRef = useRef<HTMLVideoElement>(null);
  const [playing, setPlaying] = useState(false);
 
  const toggle = () => {
    if (videoRef.current?.paused) {
      videoRef.current.play();
    } else {
      videoRef.current?.pause();
    }
  };
 
  return (
    <div>
      <video
        ref={videoRef}
        src={src}
        onPlay={() => setPlaying(true)}
        onPause={() => setPlaying(false)}
      />
      <button onClick={toggle}>{playing ? "Pause" : "Play"}</button>
    </div>
  );
}

// Image onLoad / onError
"use client";
 
import { useState } from "react";
 
export function SafeImage({ src, alt }: { src: string; alt: string }) {
  const [loaded, setLoaded] = useState(false);
  const [error, setError] = useState(false);
 
  if (error) return <div className="bg-gray-200 p-4">Failed to load image</div>;
 
  return (
    <img
      src={src}
      alt={alt}
      onLoad={() => setLoaded(true)}
      onError={() => setError(true)}
      className={loaded ? "opacity-100" : "opacity-0"}
      style={{ transition: "opacity 0.3s" }}
    />
  );
}

// Animation end callback
"use client";
 
import { useState } from "react";
 
export function FadeOutAndRemove() {
  const [visible, setVisible] = useState(true);
  const [animating, setAnimating] = useState(false);
 
  const handleDismiss = () => setAnimating(true);
 
  if (!visible) return null;
 
  return (
    <div
      className={animating ? "animate-fadeOut" : ""}
      onAnimationEnd={() => {
        if (animating) setVisible(false);
      }}
    >
      <p>I will fade away</p>
      <button onClick={handleDismiss}>Dismiss</button>
    </div>
  );
}

When to reach for this: You need to synchronize UI state with media playback, image loading lifecycle, or CSS animation/transition completion.

Working Example

// CustomVideoPlayer.tsx
"use client";
 
import { useRef, useState, useCallback } from "react";
 
export default function CustomVideoPlayer({ src }: { src: string }) {
  const videoRef = useRef<HTMLVideoElement>(null);
  const [playing, setPlaying] = useState(false);
  const [currentTime, setCurrentTime] = useState(0);
  const [duration, setDuration] = useState(0);
  const [volume, setVolume] = useState(1);
  const [muted, setMuted] = useState(false);
  const [buffering, setBuffering] = useState(false);
 
  const togglePlay = useCallback(() => {
    const video = videoRef.current;
    if (!video) return;
    if (video.paused) {
      video.play();
    } else {
      video.pause();
    }
  }, []);
 
  const handleTimeUpdate = useCallback(
    (e: React.SyntheticEvent<HTMLVideoElement>) => {
      setCurrentTime(e.currentTarget.currentTime);
    },
    []
  );
 
  const handleLoadedData = useCallback(
    (e: React.SyntheticEvent<HTMLVideoElement>) => {
      setDuration(e.currentTarget.duration);
    },
    []
  );
 
  const handleVolumeChange = useCallback(
    (e: React.SyntheticEvent<HTMLVideoElement>) => {
      setVolume(e.currentTarget.volume);
      setMuted(e.currentTarget.muted);
    },
    []
  );
 
  const handleSeek = useCallback(
    (e: React.ChangeEvent<HTMLInputElement>) => {
      const video = videoRef.current;
      if (!video) return;
      video.currentTime = Number(e.target.value);
    },
    []
  );
 
  const handleVolumeSlider = useCallback(
    (e: React.ChangeEvent<HTMLInputElement>) => {
      const video = videoRef.current;
      if (!video) return;
      video.volume = Number(e.target.value);
    },
    []
  );
 
  const toggleMute = useCallback(() => {
    const video = videoRef.current;
    if (!video) return;
    video.muted = !video.muted;
  }, []);
 
  const formatTime = (seconds: number) => {
    const m = Math.floor(seconds / 60);
    const s = Math.floor(seconds % 60);
    return `${m}:${s.toString().padStart(2, "0")}`;
  };
 
  const progress = duration > 0 ? (currentTime / duration) * 100 : 0;
 
  return (
    <div className="max-w-2xl mx-auto bg-black rounded-xl overflow-hidden">
      <div className="relative">
        <video
          ref={videoRef}
          src={src}
          className="w-full"
          onPlay={() => setPlaying(true)}
          onPause={() => setPlaying(false)}
          onTimeUpdate={handleTimeUpdate}
          onLoadedData={handleLoadedData}
          onVolumeChange={handleVolumeChange}
          onWaiting={() => setBuffering(true)}
          onSeeked={() => setBuffering(false)}
          onEnded={() => setPlaying(false)}
          onClick={togglePlay}
        />
 
        {buffering && (
          <div className="absolute inset-0 flex items-center justify-center bg-black/30">
            <div className="w-10 h-10 border-4 border-white border-t-transparent rounded-full animate-spin" />
          </div>
        )}
      </div>
 
      {/* Progress bar */}
      <div className="px-4 pt-2">
        <div className="relative h-1 bg-gray-700 rounded-full">
          <div
            className="absolute h-full bg-blue-500 rounded-full"
            style={{ width: `${progress}%` }}
          />
        </div>
        <input
          type="range"
          min={0}
          max={duration || 0}
          step={0.1}
          value={currentTime}
          onChange={handleSeek}
          className="w-full opacity-0 absolute cursor-pointer"
          style={{ marginTop: "-6px", height: "12px" }}
          aria-label="Seek"
        />
      </div>
 
      {/* Controls */}
      <div className="flex items-center gap-4 p-4 text-white">
        <button
          onClick={togglePlay}
          className="text-xl"
          aria-label={playing ? "Pause" : "Play"}
        >
          {playing ? "⏸" : "▶"}
        </button>
 
        <span className="text-sm font-mono">
          {formatTime(currentTime)} / {formatTime(duration)}
        </span>
 
        <div className="flex items-center gap-2 ml-auto">
          <button onClick={toggleMute} aria-label={muted ? "Unmute" : "Mute"}>
            {muted || volume === 0 ? "🔇" : "🔊"}
          </button>
          <input
            type="range"
            min={0}
            max={1}
            step={0.05}
            value={muted ? 0 : volume}
            onChange={handleVolumeSlider}
            className="w-20"
            aria-label="Volume"
          />
        </div>
      </div>
    </div>
  );
}

What this demonstrates:

Using onPlay, onPause, and onEnded to track playback state
Using onTimeUpdate to sync a progress bar with the current time
Using onLoadedData to capture the video duration
Using onVolumeChange to reflect volume and mute state changes
Using onWaiting and onSeeked for buffering indicator
Controlling the video element via ref while listening to events for state sync

Deep Dive

How It Works

Media events are dispatched by the browser's native <video> and <audio> elements. React wraps them as SyntheticEvent instances.
onTimeUpdate fires approximately 4 times per second during playback (browser-dependent, not tied to requestAnimationFrame).
Image onLoad fires after the image is fully decoded and ready to display. onError fires if the source URL fails.
CSS onAnimationEnd fires once per animation per element. If multiple animations run on the same element, it fires for each.
onTransitionEnd fires for each CSS property that transitions. Transitioning all properties may produce multiple events.

Variations

Image lazy loading with fade-in on load:

"use client";
 
import { useState, useCallback } from "react";
 
export function LazyImage({
  src,
  alt,
  width,
  height,
}: {
  src: string;
  alt: string;
  width: number;
  height: number;
}) {
  const [loaded, setLoaded] = useState(false);
  const [error, setError] = useState(false);
 
  const handleLoad = useCallback(() => setLoaded(true), []);
  const handleError = useCallback(() => setError(true), []);
 
  return (
    <div
      className="relative overflow-hidden bg-gray-100"
      style={{ width, height }}
    >
      {error ? (
        <div className="flex items-center justify-center w-full h-full text-gray-400">
          Failed to load
        </div>
      ) : (
        <>
          {!loaded && (
            <div className="absolute inset-0 animate-pulse bg-gray-200" />
          )}
          <img
            src={src}
            alt={alt}
            loading="lazy"
            onLoad={handleLoad}
            onError={handleError}
            className={`w-full h-full object-cover transition-opacity duration-500 ${
              loaded ? "opacity-100" : "opacity-0"
            }`}
          />
        </>
      )}
    </div>
  );
}

Animation chaining with onAnimationEnd:

"use client";
 
import { useState, useCallback } from "react";
 
type Phase = "idle" | "slideIn" | "pulse" | "slideOut" | "done";
 
export function AnimationChain() {
  const [phase, setPhase] = useState<Phase>("idle");
 
  const start = useCallback(() => setPhase("slideIn"), []);
 
  const handleAnimationEnd = useCallback(
    (e: React.AnimationEvent) => {
      // Only handle animations on this specific element
      if (e.target !== e.currentTarget) return;
 
      const transitions: Record<string, Phase> = {
        slideIn: "pulse",
        pulse: "slideOut",
        slideOut: "done",
      };
      const next = transitions[phase];
      if (next) setPhase(next);
    },
    [phase]
  );
 
  if (phase === "done") {
    return <button onClick={() => setPhase("idle")}>Reset</button>;
  }
 
  const animationClass: Record<Phase, string> = {
    idle: "",
    slideIn: "animate-slideInRight",
    pulse: "animate-pulse",
    slideOut: "animate-slideOutLeft",
    done: "",
  };
 
  return (
    <div>
      {phase === "idle" ? (
        <button onClick={start}>Start Animation Chain</button>
      ) : (
        <div
          className={`p-8 bg-blue-500 text-white rounded-lg ${animationClass[phase]}`}
          onAnimationEnd={handleAnimationEnd}
        >
          Phase: {phase}
        </div>
      )}
    </div>
  );
}

Transition completion callback:

"use client";
 
import { useState, useCallback } from "react";
 
export function CollapsePanel({
  children,
  title,
}: {
  children: React.ReactNode;
  title: string;
}) {
  const [open, setOpen] = useState(false);
  const [rendered, setRendered] = useState(false);
 
  const toggle = useCallback(() => {
    if (!open) {
      setRendered(true); // mount content before expanding
      requestAnimationFrame(() => setOpen(true));
    } else {
      setOpen(false);
    }
  }, [open]);
 
  const handleTransitionEnd = useCallback(
    (e: React.TransitionEvent) => {
      // Only respond to height transition, not other properties
      if (e.propertyName === "max-height" && !open) {
        setRendered(false); // unmount after collapse completes
      }
    },
    [open]
  );
 
  return (
    <div className="border rounded-lg">
      <button onClick={toggle} className="w-full p-4 text-left font-semibold">
        {title} {open ? "▲" : "▼"}
      </button>
      <div
        className="overflow-hidden transition-[max-height] duration-300 ease-in-out"
        style={{ maxHeight: open ? "500px" : "0px" }}
        onTransitionEnd={handleTransitionEnd}
      >
        {rendered && <div className="p-4 border-t">{children}</div>}
      </div>
    </div>
  );
}

Audio visualization basics:

"use client";
 
import { useRef, useCallback, useEffect, useState } from "react";
 
export function AudioVisualizer({ src }: { src: string }) {
  const audioRef = useRef<HTMLAudioElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);
  const analyserRef = useRef<AnalyserNode | null>(null);
  const [initialized, setInitialized] = useState(false);
 
  const initAudio = useCallback(() => {
    if (initialized || !audioRef.current) return;
    const ctx = new AudioContext();
    const source = ctx.createMediaElementSource(audioRef.current);
    const analyser = ctx.createAnalyser();
    analyser.fftSize = 256;
    source.connect(analyser);
    analyser.connect(ctx.destination);
    analyserRef.current = analyser;
    setInitialized(true);
  }, [initialized]);
 
  useEffect(() => {
    if (!initialized) return;
    const analyser = analyserRef.current;
    const canvas = canvasRef.current;
    if (!analyser || !canvas) return;
 
    const ctx = canvas.getContext("2d");
    if (!ctx) return;
 
    const bufferLength = analyser.frequencyBinCount;
    const dataArray = new Uint8Array(bufferLength);
 
    let animationId: number;
    const draw = () => {
      animationId = requestAnimationFrame(draw);
      analyser.getByteFrequencyData(dataArray);
 
      ctx.fillStyle = "#000";
      ctx.fillRect(0, 0, canvas.width, canvas.height);
 
      const barWidth = (canvas.width / bufferLength) * 2.5;
      let x = 0;
      for (let i = 0; i < bufferLength; i++) {
        const barHeight = (dataArray[i] / 255) * canvas.height;
        ctx.fillStyle = `hsl(${(i / bufferLength) * 360}, 80%, 50%)`;
        ctx.fillRect(x, canvas.height - barHeight, barWidth, barHeight);
        x += barWidth + 1;
      }
    };
    draw();
 
    return () => cancelAnimationFrame(animationId);
  }, [initialized]);
 
  return (
    <div className="space-y-4">
      <canvas ref={canvasRef} width={600} height={200} className="bg-black rounded-lg" />
      <audio
        ref={audioRef}
        src={src}
        controls
        onPlay={initAudio}
        crossOrigin="anonymous"
      />
    </div>
  );
}

Video progress bar with preview:

"use client";
 
import { useRef, useState, useCallback } from "react";
 
export function VideoProgressBar({
  videoRef,
  duration,
  currentTime,
}: {
  videoRef: React.RefObject<HTMLVideoElement | null>;
  duration: number;
  currentTime: number;
}) {
  const barRef = useRef<HTMLDivElement>(null);
  const [hoverTime, setHoverTime] = useState<number | null>(null);
 
  const handleClick = useCallback(
    (e: React.MouseEvent<HTMLDivElement>) => {
      const rect = e.currentTarget.getBoundingClientRect();
      const fraction = (e.clientX - rect.left) / rect.width;
      if (videoRef.current) {
        videoRef.current.currentTime = fraction * duration;
      }
    },
    [videoRef, duration]
  );
 
  const handleMouseMove = useCallback(
    (e: React.MouseEvent<HTMLDivElement>) => {
      const rect = e.currentTarget.getBoundingClientRect();
      const fraction = (e.clientX - rect.left) / rect.width;
      setHoverTime(fraction * duration);
    },
    [duration]
  );
 
  const progress = duration > 0 ? (currentTime / duration) * 100 : 0;
 
  const formatTime = (s: number) =>
    `${Math.floor(s / 60)}:${Math.floor(s % 60)
      .toString()
      .padStart(2, "0")}`;
 
  return (
    <div
      ref={barRef}
      className="relative h-2 bg-gray-700 rounded cursor-pointer group"
      onClick={handleClick}
      onMouseMove={handleMouseMove}
      onMouseLeave={() => setHoverTime(null)}
    >
      <div
        className="h-full bg-blue-500 rounded"
        style={{ width: `${progress}%` }}
      />
      {hoverTime !== null && (
        <div
          className="absolute -top-8 bg-black text-white text-xs px-2 py-1 rounded -translate-x-1/2"
          style={{ left: `${(hoverTime / duration) * 100}%` }}
        >
          {formatTime(hoverTime)}
        </div>
      )}
    </div>
  );
}

TypeScript Notes

// Media event -- typed to the specific element
function handlePlay(e: React.SyntheticEvent<HTMLVideoElement>) {
  const video: HTMLVideoElement = e.currentTarget;
  const time: number = video.currentTime;
  const dur: number = video.duration;
  const paused: boolean = video.paused;
  const vol: number = video.volume;
}
 
// Audio element events use the same type
function handleAudioEnd(e: React.SyntheticEvent<HTMLAudioElement>) {
  const audio: HTMLAudioElement = e.currentTarget;
  console.log("Audio ended at", audio.duration);
}
 
// Image load/error
function handleImgLoad(e: React.SyntheticEvent<HTMLImageElement>) {
  const img: HTMLImageElement = e.currentTarget;
  const naturalWidth: number = img.naturalWidth;
  const naturalHeight: number = img.naturalHeight;
}
 
// Animation events
function handleAnimEnd(e: React.AnimationEvent<HTMLDivElement>) {
  const name: string = e.animationName; // CSS animation name
  const elapsed: number = e.elapsedTime; // seconds
  const pseudo: string = e.pseudoElement; // "::before", "::after", or ""
}
 
// Transition events
function handleTransEnd(e: React.TransitionEvent<HTMLDivElement>) {
  const property: string = e.propertyName; // e.g., "opacity", "transform"
  const elapsed: number = e.elapsedTime; // seconds
  const pseudo: string = e.pseudoElement;
}
 
// Ref typing for media elements
const videoRef = useRef<HTMLVideoElement>(null);
const audioRef = useRef<HTMLAudioElement>(null);

Gotchas

onTransitionEnd fires once per property -- Transitioning all or multiple properties (e.g., opacity and transform) fires the event multiple times. Fix: Check e.propertyName to respond only to the property you care about: if (e.propertyName !== "opacity") return;.
onAnimationEnd bubbles from child elements -- If a child has its own CSS animation, the event bubbles up to your handler. Fix: Compare e.target === e.currentTarget to ensure you only respond to your element's animation.
onTimeUpdate does not fire every frame -- It fires roughly 4 times per second, not 60. This makes it too coarse for frame-accurate UI. Fix: For smooth progress bars, use requestAnimationFrame with videoRef.current.currentTime instead.
Media onError gives minimal information -- The SyntheticEvent does not include an error code directly. Fix: Access e.currentTarget.error (a MediaError object) with e.currentTarget.error?.code and e.currentTarget.error?.message for details.
onLoad on <img> fires on cached images too -- But the timing is different: cached images may fire onLoad synchronously during render. Fix: Always initialize your loading state to false and let onLoad set it to true, rather than assuming async timing.
CSS animations on unmounted elements do not fire onAnimationEnd -- If you remove the element from the DOM before the animation finishes, the event never fires. Fix: Wait for onAnimationEnd before setting the state that removes the element, or use the Web Animations API for promise-based control.
play() returns a Promise that can reject -- Calling videoRef.current.play() returns a Promise. If the user has not interacted with the page, autoplay policies reject it. Fix: Always await or .catch() the play promise: videoRef.current.play().catch(() => { /* handle autoplay block */ }).

Alternatives

Alternative	Use When	Don't Use When
Web Animations API (`element.animate()`)	You need JS-driven animations with promises and playback control	CSS keyframes are sufficient
Framer Motion (`motion.div`)	You want declarative React animations with enter/exit/layout	You only need to handle native media events
`requestAnimationFrame`	You need frame-accurate progress tracking for video	`onTimeUpdate` precision is acceptable
`<video>` with HLS.js / dash.js	You need adaptive streaming (ABR)	A single MP4 file works fine
Next.js `<Image>`	You want automatic optimization, lazy loading, and blur placeholder	You need fine-grained `onLoad` / `onError` control with custom logic

FAQs

How do I detect when a video is buffering?

Use onWaiting to detect when playback stalls due to insufficient data
Use onSeeked or onCanPlay to detect when enough data is available to resume
Show a loading spinner between onWaiting and the next onSeeked/onCanPlay

Why does video.play() sometimes throw an error?

Browser autoplay policies require user interaction before media can play with sound
play() returns a Promise that rejects if autoplay is blocked
Always handle the rejection: video.play().catch(() => { /* show play button */ })
Videos with muted attribute are usually allowed to autoplay

How do I chain multiple CSS animations on the same element?

Listen to onAnimationEnd and change the CSS class to trigger the next animation
Check e.animationName to know which animation just finished
Set state to apply the next animation class, creating a sequential chain

Why does onTransitionEnd fire multiple times?

It fires once per CSS property that transitions
If you transition transform and opacity, you get two events
Filter by e.propertyName to respond only to the one you care about

How do I build a custom progress bar for a video player?

Use onLoadedData to get video.duration
Use onTimeUpdate to track video.currentTime
Calculate (currentTime / duration) * 100 for the progress percentage
For smoother updates, use requestAnimationFrame instead of onTimeUpdate

How do I handle image loading errors gracefully?

const [error, setError] = useState(false);
 
return error ? (
  <div className="placeholder">Image unavailable</div>
) : (
  <img
    src={src}
    alt={alt}
    onError={() => setError(true)}
  />
);

Can I detect when a CSS animation loops with onAnimationIteration?

Yes, onAnimationIteration fires at the end of each iteration for animations with animation-iteration-count greater than 1
It does not fire at the end of the last iteration -- use onAnimationEnd for that
The event includes animationName and elapsedTime to identify which cycle completed

Pointer Events -- Unified input across mouse, touch, and pen
Touch Events -- Multi-touch gesture handling for mobile
Scroll Events -- Scroll position tracking and infinite scroll

Media & Animation Events

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Media & Animation Events