FileReaderSync: readAsBinaryString() method

Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

Note: This feature is only available in Web Workers, except for Service Workers.

Note: This method is deprecated in favor of readAsArrayBuffer().

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





The File or Blob to read.

Return value

A string representing the input data.


NotFoundError DOMException

Thrown if the resource represented by the DOM File or Blob cannot be found, e.g. because it has been erased.

SecurityError DOMException

Thrown if one of the following problematic situation is detected:

  • the resource has been modified by a third party;
  • too many read are performed simultaneously;
  • the file pointed by the resource is unsafe for a use from the Web (like it is a system file).
NotReadableError DOMException

Thrown if the resource cannot be read due to a permission problem, like a concurrent lock.

EncodingError DOMException

Thrown if the resource is a data URL and exceed the limit length defined by each browser.


File API
# readAsBinaryStringSyncSection

Browser compatibility

BCD tables only load in the browser

See also