Re: [w3c/clipboard-apis] Selective Clipboard Format Read (Issue #240)

roraja left a comment (w3c/clipboard-apis#240)

I've been thinking more about the lazy `getType()` approach (Option 2) and want to raise some concerns about what this does to ClipboardItem's semantics.

The core issue is that lazy `getType()` transforms ClipboardItem from a **data object** (snapshot of clipboard at read-time) to a **service proxy** (lazy fetcher that may fail if clipboard changed). This is a fundamental semantic shift which might confuse web developers.

Consider the current interface:

```jsx
readonly attribute FrozenArray<DOMString> types;
Promise<Blob> getType(DOMString type);
```

The `types` property is a `FrozenArray`—explicitly immutable—which signals to developers: "these types are fixed and available." But with lazy `getType()`, this becomes misleading. A developer might see `types` includes `"text/plain"`, call `getType("text/plain")`, and get an error/empty data because the clipboard changed. The `FrozenArray` implied availability that doesn't exist.

More fundamentally, the spec describes ClipboardItem as:

> "conceptually data that the user has expressed a desire to make shareable by invoking a 'cut' or 'copy' command."
> 

This is snapshot language—data from a past action. Lazy `getType()` changes this to: "a handle to whatever is currently on the clipboard, which may or may not match what was there when you called read()."

However, if a web developer creates a new ClipboardItem for writing purpose, then the semantic meaning again switches back to being a “fronzen data container”, further adding to the confusion for web developers and creating inconsistency in the interface.

```jsx
// This now acts like a frozen data object, getType won't error out if clipboard changes
const item = new ClipboardItem({ "txt/plain": "My text", “txt/html”: “My html” })
navigator.clipboard.write(item)
```

So "ClipboardItem" now behaves both like a frozen data object when created explicitly by web author and also like a service proxy which fetches latest data or empty data if the clipboard changed after read() call. I think makes the API look not simple to understand and unintuitive as the web developer has to understand all these special cases under which the behavior changes.

Any thoughts ?

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