FileReader: readAsText() method

Available in 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 property 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 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

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

<input type="file" /><br />
<p class="content"></p>

JavaScript

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

fileInput.addEventListener("change", previewFile);

function previewFile() {
  const file = fileInput.files[0];
  const reader = new FileReader();

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

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

Result

Specifications

Browser compatibility

See also

• FileReader