kpozin kpozin - 1 year ago 96
Javascript Question

Converting between strings and ArrayBuffers

Is there a commonly accepted technique for efficiently converting JavaScript strings to ArrayBuffers and vice-versa? Specifically, I'd like to be able to write the contents of an ArrayBuffer to

and to read it back.

Answer Source

Although Dennis and gengkev solutions of using Blob/FileReader work, I wouldn't suggest taking that approach. It is a async approach to a simple problem, and it is much slower than a direct solution. I've made a post in html5rocks with a simpler and (much faster) solution:

And the solution is:

function ab2str(buf) {
  return String.fromCharCode.apply(null, new Uint16Array(buf));

function str2ab(str) {
  var buf = new ArrayBuffer(str.length*2); // 2 bytes for each char
  var bufView = new Uint16Array(buf);
  for (var i=0, strLen=str.length; i<strLen; i++) {
    bufView[i] = str.charCodeAt(i);
  return buf;


The Encoding API helps solving the string conversion problem. Check out the response from Jeff Posnik on to the above original article.


The Encoding API makes it simple to translate between raw bytes and native JavaScript strings, regardless of which of the many standard encodings you need to work with.

<pre id="results"></pre>

  if ('TextDecoder' in window) {
    // The local files to be fetched, mapped to the encoding that they're using.
    var filesToEncoding = {
      'utf8.bin': 'utf-8',
      'utf16le.bin': 'utf-16le',
      'macintosh.bin': 'macintosh'

    Object.keys(filesToEncoding).forEach(function(file) {
      fetchAndDecode(file, filesToEncoding[file]);
  } else {
    document.querySelector('#results').textContent = 'Your browser does not support the Encoding API.'

  // Use XHR to fetch `file` and interpret its contents as being encoded with `encoding`.
  function fetchAndDecode(file, encoding) {
    var xhr = new XMLHttpRequest();'GET', file);
    // Using 'arraybuffer' as the responseType ensures that the raw data is returned,
    // rather than letting XMLHttpRequest decode the data first.
    xhr.responseType = 'arraybuffer';
    xhr.onload = function() {
      if (this.status == 200) {
        // The decode() method takes a DataView as a parameter, which is a wrapper on top of the ArrayBuffer.
        var dataView = new DataView(this.response);
        // The TextDecoder interface is documented at
        var decoder = new TextDecoder(encoding);
        var decodedString = decoder.decode(dataView);
        // Add the decoded file's text to the <pre> element on the page.
        document.querySelector('#results').textContent += decodedString + '\n';
      } else {
        console.error('Error while requesting', file, this);