No, decodeAudioData in JavaScript does not detach the ArrayBuffer passed as an argument.

When you call decodeAudioData(arrayBuffer) on an AudioContext, it decodes the audio file contained in the ArrayBuffer into an AudioBuffer. After this operation, the ArrayBuffer remains available for use; it is not detached or made unusable. This behavior allows you to reuse the ArrayBuffer after decoding, if necessary.

However, the internal data of the ArrayBuffer is copied during the decoding process, which means the decoding itself doesn't modify the original buffer.

In contrast, certain methods (like postMessage with transferable objects) may explicitly detach buffers, but decodeAudioData is not one of them.

ArrayBuffer.detached becoming true after calling decodeAudioData on it may indicate that the environment you're working in (like a particular browser version or a specific JavaScript engine) is detaching the ArrayBuffer as part of the internal optimization or implementation of decodeAudioData. However, this behavior isn't mandated by the specification, and it can depend on how the underlying platform handles memory management.

Possible Reasons for ArrayBuffer Detachment:

1. Internal Optimization: Some browsers or JavaScript engines may detach the ArrayBuffer after decoding to free up memory as soon as possible, ensuring that once it's been decoded, the raw data isn't needed anymore.

2. Transferable Objects Mechanism: In some scenarios, certain JavaScript APIs (such as postMessage with transferable objects) can "transfer" ownership of the ArrayBuffer and mark it as detached to prevent further access. This might be happening behind the scenes with decodeAudioData, depending on the browser's implementation.

3. Spec/Implementation Changes: Although the spec doesn't explicitly require the ArrayBuffer to be detached after decoding, changes or optimizations in the browser's implementation may result in such behavior.

What Happens When ArrayBuffer is Detached?

When an ArrayBuffer is detached:

• Its byteLength is set to 0.
• It becomes unusable, meaning attempts to access its data will result in an empty buffer or throw errors.

How to Handle This:

If you're experiencing ArrayBuffer detachment after calling decodeAudioData, a workaround would be to create a copy of the ArrayBuffer before decoding it if you need to reuse it afterward:

javascript
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let originalBuffer = /* your ArrayBuffer */;
let copyBuffer = originalBuffer.slice(0); // Creates a copy of the ArrayBuffer

audioContext.decodeAudioData(copyBuffer, (audioBuffer) => {
  // Decoding process...
});

This ensures the original ArrayBuffer remains intact even if the copy is detached during decoding.

In summary, while decodeAudioData is not expected to detach the ArrayBuffer according to the standard specification, some browser implementations may do so for optimization. Creating a copy of the ArrayBuffer beforehand can help avoid this issue.

The behavior you're observing—ArrayBuffer.detached changing from false to true after calling decodeAudioData—is indeed interesting, but it's important to note that the detached property of ArrayBuffer isn't a standard property in JavaScript according to the current ECMAScript specification.

Understanding What’s Happening:

1. ArrayBuffer.detached:

   • detached is a non-standard feature that some browsers (like Chrome, Edge, and Firefox) might use internally as an optimization mechanism.
   • The fact that this property exists and changes to true in your case suggests that these browsers are detaching the ArrayBuffer behind the scenes when passing it to decodeAudioData.

2. Detachment in decodeAudioData:

   • When you pass an ArrayBuffer to decodeAudioData, it's possible that the browser internally transfers ownership of that buffer or optimizes memory usage by marking the buffer as detached after it has been processed.
   • Once the ArrayBuffer is detached, its internal memory becomes inaccessible, and its byteLength is set to 0. This prevents further use of the ArrayBuffer and frees up memory.

3. Browser-Specific Behavior:

   • The behavior you see in Edge, Chrome, and Firefox is likely an implementation detail specific to those browsers. The JavaScript specification doesn't require decodeAudioData to detach the ArrayBuffer. However, these browsers might be doing so to optimize memory usage or manage resources more efficiently.

Example:

javascript
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const ab = new ArrayBuffer(1024);
const audioContext = new AudioContext();

console.log("%o", ab.detached); // Outputs: false
audioContext.decodeAudioData(ab).then(() => {
    console.log("%o", ab.detached); // Outputs: true in Chrome, Edge, Firefox
});

Why This Happens:

• Memory Optimization: By detaching the ArrayBuffer, browsers can avoid keeping both the original binary data and the decoded AudioBuffer in memory at the same time. This helps reduce memory usage in resource-heavy applications, such as when decoding large audio files.

• Transferable Objects: Detachment of the ArrayBuffer may be treated similarly to how the postMessage API transfers ownership of an ArrayBuffer, making the original buffer unavailable.

Cross-Browser Consideration:

• While Chrome, Edge, and Firefox might show this behavior, other browsers (like Safari or others in the future) might not detach the ArrayBuffer. Therefore, relying on this behavior in production code is risky because it's not part of the ECMAScript standard.

Solution if You Need to Reuse the ArrayBuffer:

If you need to reuse the ArrayBuffer after decoding (or avoid detachment altogether), you can make a copy of the ArrayBuffer before passing it to decodeAudioData:

javascript
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const ab = new ArrayBuffer(1024);
const abCopy = ab.slice(0); // Create a copy of the buffer

const audioContext = new AudioContext();
audioContext.decodeAudioData(abCopy).then((audioBuffer) => {
    console.log("Decoded successfully");
});

console.log("%o", ab.detached); // false, the original buffer is not detached

In this case, the original ArrayBuffer remains intact, and you can continue using it after the decoding operation.

Conclusion:

The behavior you're seeing is an optimization technique used by browsers like Chrome, Edge, and Firefox, but it's not guaranteed across all browsers. The ArrayBuffer detachment is not required by the standard, so the safest approach if you need to reuse the buffer is to create a copy before decoding.