FileReader.result

The FileReader result property returns the file's contents. This property is only valid after the read operation is complete, and the format of the data depends on which of the methods was used to initiate the read operation.

Value

An appropriate string or ArrayBuffer based on which of the reading methods was used to initiate the read operation. The value is null if the reading is not yet complete or was unsuccessful.

The result types are described below.

Method Description
readAsArrayBuffer() The result is a JavaScript ArrayBuffer containing binary data.
readAsBinaryString() The result contains the raw binary data from the file in a string.
readAsDataURL() The result is a string with a data: URL representing the file's data.
readAsText() The result is text in a string.

Examples

This example presents a function, read(), which reads a file from a file input. It works by creating a FileReader object and creating a listener for load events such that when then file is read, the result is obtained and passed to the callback function provided to read().

The content is handled as raw text data.

const fileInput = document.querySelector('input[type="file"]');

function read(callback) {
  const file = fileInput.files.item(0);
  const reader = new FileReader();

  reader.onload = () => {
    callback(reader.result);
  }

  reader.readAsText(file);
}

Specifications

Specification
File API
# dom-filereader-result

Browser compatibility

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See also