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For a browser audio element, use canplay to detect when the browser believes playback can begin. That does not mean the entire file has downloaded. Use loadedmetadata for details such as duration, canplaythrough for the browser’s estimate that playback can continue to the end, and fetch() when you specifically need to consume the full response.
Choose the signal that matches what “loaded” means
Audio loading is not a single state. A browser can know a track’s duration before it has enough audio data to play, and it can begin playback before the complete file has arrived. The media events and readyState property describe these different stages. Their timing can vary with caching, network conditions, streaming, and browser settings. See MDN’s HTMLMediaElement reference.
| If you need to know… | Use | What it means |
|---|---|---|
| Whether loading has begun | loadstart |
The browser started loading; usable audio is not guaranteed. |
| Whether duration or other metadata is available | loadedmetadata |
Metadata is available, but playback may not yet be possible. |
| Whether initial media data is available | loadeddata |
Data for the current position is available. This event may not fire on some mobile devices in data-saving mode. |
| Whether playback can start | canplay |
The browser estimates it can begin playback, though more data may be needed later. |
| Whether playback can probably continue to the end without buffering | canplaythrough |
The browser estimates enough data is available. This is not proof that every byte has downloaded. |
| Whether a load failed | error |
The resource could not be loaded; inspect audio.error for the media error. |
For most players, canplay is the useful signal for enabling a Play button. For the event definitions, see MDN on canplay, canplaythrough, and loadeddata.
A robust pattern for a dynamically created audio element
Register listeners before assigning the source. This avoids application-level timing problems if a cached or very small file becomes ready quickly. Handle failure as well as success:
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function loadAudio(url) {
return new Promise((resolve, reject) => {
const audio = new Audio();
audio.preload = "auto";
const cleanup = () => {
audio.removeEventListener("canplay", onReady);
audio.removeEventListener("error", onError);
};
const onReady = () => {
cleanup();
resolve(audio);
};
const onError = () => {
cleanup();
reject(audio.error ?? new Error(`Unable to load ${url}`));
};
audio.addEventListener("canplay", onReady, { once: true });
audio.addEventListener("error", onError, { once: true });
audio.src = url;
audio.load();
});
}
loadAudio("/audio/effect.mp3")
.then((audio) => {
console.log("Ready to start");
return audio.play();
})
.catch((error) => {
console.error("Audio loading or playback failed:", error);
});Readiness and permission to play are separate. A browser can allow the file to load but reject script-initiated playback under its autoplay rules. The promise returned by play() should therefore be handled; a NotAllowedError commonly means user interaction is needed. See MDN’s HTMLMediaElement documentation.
Using an audio element already in the page
If you need the duration for a timeline or track label, wait for loadedmetadata. Enable playback on canplay instead:
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<audio id="player" preload="metadata">
<source src="/audio/theme.mp3" type="audio/mpeg">
</audio>
<button id="play" disabled>Play</button>
<script>
const player = document.querySelector("#player");
const playButton = document.querySelector("#play");
player.addEventListener("loadedmetadata", () => {
console.log(`Duration: ${player.duration} seconds`);
});
player.addEventListener("canplay", () => {
playButton.disabled = false;
});
player.addEventListener("error", () => {
console.error("Media error:", player.error?.code, player.error?.message);
});
</script>preload="metadata" suits a page that needs media details but does not want to request the entire file eagerly. preload="auto" expresses a preference to preload more, while preload="none" asks the browser not to preload. These are hints, not guarantees that the browser will download a particular amount. See MDN on the preload property.
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You can also create an element explicitly and set listeners before its source:
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const audio = document.createElement("audio");
audio.preload = "auto";
audio.addEventListener("canplay", () => console.log("Ready"), { once: true });
audio.addEventListener("error", () => console.error("Load failed", audio.error), { once: true });
audio.src = "/audio/menu-click.mp3";
audio.load();new Audio(url) is shorter, but passing a URL starts loading asynchronously, so attach listeners promptly. For maximum control, construct without a URL, set preload, add listeners, then assign src. The constructor creates an HTMLAudioElement; see MDN’s Audio() reference. Calling load() resets source selection and starts loading; if called during an active load, it interrupts that operation. Use it when changing a source, not as a routine extra call. See MDN on load().
Check the current state with readyState
If loading may already have started before your code runs, check the current value rather than waiting only for a future event:
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if (audio.readyState >= HTMLMediaElement.HAVE_FUTURE_DATA) {
console.log("Enough data is available to begin playback");
}| Constant | Value | Meaning |
|---|---|---|
HAVE_NOTHING |
0 | No usable media information is available. |
HAVE_METADATA |
1 | Metadata is available. |
HAVE_CURRENT_DATA |
2 | Data is available for the current playback position. |
HAVE_FUTURE_DATA |
3 | Enough data exists to begin playback and continue briefly. |
HAVE_ENOUGH_DATA |
4 | The browser estimates it can play through without interruption. |
Use HAVE_FUTURE_DATA as the practical threshold for “ready to start”; HAVE_ENOUGH_DATA is the stronger browser estimate, not a guarantee. The state can change as playback and network conditions change. See MDN’s readyState reference.
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If you truly need the entire response downloaded
Neither canplay nor canplaythrough proves byte-for-byte completion. If the app must process or retain the whole response—for example, for a short sound effect that it will hash or decode—fetch it and consume the body:
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async function fetchAudioCompletely(url) {
const response = await fetch(url);
if (!response.ok) throw new Error(`HTTP ${response.status}`);
return response.arrayBuffer();
}
const bytes = await fetchAudioCompletely("/audio/effect.mp3");
const blobUrl = URL.createObjectURL(new Blob([bytes], { type: "audio/mpeg" }));
const audio = new Audio(blobUrl);
await new Promise((resolve, reject) => {
audio.addEventListener("canplay", resolve, { once: true });
audio.addEventListener("error", () => reject(audio.error), { once: true });
});Consuming arrayBuffer() means the fetch response body has been read to completion; the subsequent canplay confirms the media element can start playback. This approach holds the response in memory, which grows with file size, and cross-origin requests require suitable CORS permission. It is generally a poor fit for long tracks or streaming playback. If you need decoded samples for Web Audio rather than an audio element, pass the bytes to AudioContext.decodeAudioData(); successful decoding is a different condition from media-element readiness.
Preloading several effects
For a small set of game or interface sounds, resolve each promise only when that sound reaches the readiness level your app needs, and reject failures instead of leaving a loading screen waiting forever:
function preloadAudio(urls) {
return Promise.all(urls.map((url) => new Promise((resolve, reject) => {
const audio = new Audio();
audio.preload = "auto";
const cleanup = () => {
audio.removeEventListener("canplay", onReady);
audio.removeEventListener("error", onError);
};
const onReady = () => { cleanup(); resolve(audio); };
const onError = () => { cleanup(); reject(new Error(`Failed to load ${url}`)); };
audio.addEventListener("canplay", onReady, { once: true });
audio.addEventListener("error", onError, { once: true });
audio.src = url;
})));
}
preloadAudio(["/audio/click.mp3", "/audio/explosion.ogg", "/audio/jump.wav"])
.then((sounds) => console.log(`${sounds.length} sounds are ready`))
.catch(console.error);Promise.all() rejects as soon as any one load fails. If the interface should keep usable sounds and report individual failures, catch per-file errors and collect results instead. For a visible progress count, increment once per settled file, whether it loaded or failed. Many preloaded elements can consume bandwidth and memory; avoid eagerly loading a large library, and provide cancellation or cleanup when a component is removed.
Troubleshooting when readiness never arrives
- Check the URL and response: a typo, 404, redirect, or authentication failure can prevent loading. Inspect the browser Network panel.
- Check format and encoding: the browser may not support the codec, or the file may be malformed. With multiple
<source>options, listen for the final error on the audio element; it fires after all source choices fail. See MDN’s audio element reference. - Check server headers and cross-origin access: a wrong MIME type can cause problems, and cross-origin access restrictions matter especially when using
fetch(). Verify the server’s response and CORS configuration. - Inspect the element: log
currentSrc,readyState,networkState,duration, anderrorto see what source was selected and what state it reached. - Do not wait on the wrong event:
loadedmetadatadoes not mean playable;loadeddatacan be absent under some mobile data-saving settings. Prefercanplayfor starting playback. - Check whether your code restarted loading: changing
srcor callingload()can abort the current operation and begin another. - Separate loading from playback: if
canplayfired butplay()rejects, inspect the rejected promise; autoplay restrictions are not load errors.
console.log({
currentSrc: audio.currentSrc,
readyState: audio.readyState,
networkState: audio.networkState,
duration: audio.duration,
error: audio.error
});The browser’s usual event flow includes loadstart, loadedmetadata, loadeddata, progress, canplay, and possibly canplaythrough, but do not depend on every event arriving in one fixed sequence. Cached resources, interruptions, and browser policies affect the timing. See MDN’s cross-browser audio guide.
Quick Recap
Quick decision guide
- Need duration? Wait for
loadedmetadata. - Need to enable Play? Wait for
canplay, or check forHAVE_FUTURE_DATA. - Want the browser’s best estimate of uninterrupted playback? Use
canplaythrough, but do not treat it as a full-download guarantee. - Need the complete response body for processing? Use
fetch()and consume it, accounting for CORS and memory. - Need to know whether loading failed? Listen for
errorand inspectaudio.error.
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