Understand what an object URL represents
URL.createObjectURL creates a browser-managed URL for a Blob or File. It gives an image element or download link something it can reference without uploading the file to a server. That URL is a temporary handle, not a durable path to the original document. Do not store it as a permanent database value or assume it will work in another browser session.
Give the URL a clear owner
Consider an avatar preview where the visitor chooses a file several times. Each choice can create a new object URL. Keep the active URL with the component or operation that displays it. When replacing the preview, retire the previous handle after it is no longer needed. Ownership should be obvious enough that another feature cannot accidentally revoke a URL still used by a download control.
Revoke only after the interaction is finished
Calling revokeObjectURL immediately after assigning a preview can break loading or later user actions. Instead, connect cleanup to the preview being replaced, removed or unmounted. A generated download link may need its URL to remain valid while the link is available. The right lifetime follows the visible feature, not an arbitrary timeout guessed to be long enough.
Handle failures and replacement races
A failed conversion should not leave a download button pointing to an earlier file while describing the new input. Clear or label stale results deliberately. If conversions can overlap, ensure that a slower old operation cannot install a new active URL after a newer operation has finished. Cancellation or an operation identifier can keep result ownership aligned with the current selection.
Distinguish other URL representations
A data URL embeds encoded data in the string, while an object URL refers to browser-managed data. They have different size and lifecycle characteristics. Do not call revokeObjectURL on every arbitrary URL as a generic cleanup ritual. Keep the representation visible in the code contract, especially when a QR generator produces data URLs while an image converter produces Blob-backed URLs.
Verify repeated selection behavior
Choose several files in succession, remove a preview, generate a replacement output and navigate away. Confirm that the currently displayed image and filename still agree. Inspect memory during a longer sequence if large files are involved. A single successful preview proves little about cleanup; the useful check is whether repeated use remains stable and old resources become eligible for release.
Further reading
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