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FileReaderSync: readAsDataURL() method

files/en-us/web/api/filereadersync/readasdataurl/index.md

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{{APIRef("File API")}} {{AvailableInWorkers("worker_except_service")}}

The readAsDataURL() method of the {{DOMxRef("FileReaderSync")}} interface allows to read {{DOMxRef("File")}} or {{DOMxRef("Blob")}} objects in a synchronous way into a string representing a data URL. This interface is only available in workers as it enables synchronous I/O that could potentially block.

Syntax

js-nolint
readAsDataURL(blob)

Parameters

  • blob
    • : The {{DOMxRef("File")}} or {{DOMxRef("Blob")}} to read.

Return value

A string representing the input data as a data URL.

Exceptions

The following exceptions can be raised by this method:

  • NotFoundError {{domxref("DOMException")}}
    • : Thrown if the resource represented by the DOM {{DOMxRef("File")}} or {{DOMxRef("Blob")}} cannot be found, e.g., because it has been erased.
  • SecurityError {{domxref("DOMException")}}
    • : Thrown if one of the following problematic situation is detected:
      • the resource has been modified by a third party;
      • too many read operations are performed simultaneously;
      • the file pointed by the resource is unsafe for a use from the Web (like it is a system file).
  • NotReadableError {{domxref("DOMException")}}
    • : Thrown if the resource cannot be read due to a permission problem, like a concurrent lock.
  • EncodingError {{domxref("DOMException")}}
    • : Thrown if the resource is a data URL and exceed the limit length defined by each browser.

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also