FileReader: readAsText() method

Note: This feature is available in Web Workers

The readAsText() method of the FileReader interface is used to read the contents of the specified Blob or File. When the read operation is complete, the readyState is changed to DONE, the loadend event is triggered, and the result property contains the contents of the file as a text string.

Note: The Blob.text() method is a newer promise-based API to read a file as text.

Note: This method loads the entire file's content into memory and is not suitable for large files. Prefer readAsArrayBuffer() for large files.

Syntax

js

readAsText(blob)
readAsText(blob, encoding)

Parameters

blob

The Blob or File from which to read.

encoding Optional

A string specifying the encoding to use for the returned data. By default, UTF-8 is assumed if this parameter is not specified.

Return value

None (undefined).

Examples

HTML

html

<input type="file" onchange="previewFile()" /><br />
<p class="content"></p>

JavaScript

js

function previewFile() {
  const content = document.querySelector(".content");
  const [file] = document.querySelector("input[type=file]").files;
  const reader = new FileReader();

  reader.addEventListener(
    "load",
    () => {
      // this will then display a text file
      content.innerText = reader.result;
    },
    false,
  );

  if (file) {
    reader.readAsText(file);
  }
}

Result

Specifications

Specification
File API
# readAsDataText

Browser compatibility

BCD tables only load in the browser

See also