FileReader: readAsBinaryString() method - Web APIs | MDN (original) (raw)

Note: This feature is available in Web Workers.

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.

The readAsBinaryString() method of the FileReader interface is used to start reading the contents of the specified Blob or File. When the read operation is finished, the readyState property becomesDONE, and the loadend event is triggered. At that time, theresult property contains the raw binary data from the file.

Note that this method was once removed from the File API specification, but re-introduced for backward compatibility. Using FileReader.readAsArrayBuffer() is recommended.

Syntax

Parameters

blob

The Blob or File from which to read.

Return value

Examples

const canvas = document.createElement("canvas");
const height = 200;
const width = 200;

canvas.width = width;
canvas.height = height;

const ctx = canvas.getContext("2d");

ctx.strokeStyle = "#090";
ctx.beginPath();
ctx.arc(width / 2, height / 2, width / 2 - width / 10, 0, Math.PI * 2);
ctx.stroke();

canvas.toBlob((blob) => {
  const reader = new FileReader();

  reader.onload = () => {
    console.log(reader.result);
  };

  reader.readAsBinaryString(blob);
});

Specifications

Browser compatibility

See also