Fallback version for ie9 and others

[jimmywarting]

Please consider adding this fallback version if blob is unsupported

function FakeBlobBuilder() {

  function toUTF8Array(str) {
    var utf8 = [];
    for (var i=0; i < str.length; i++) {
      var charcode = str.charCodeAt(i);
      if (charcode < 0x80) utf8.push(charcode);
      else if (charcode < 0x800) {
        utf8.push(0xc0 | (charcode >> 6), 
        0x80 | (charcode & 0x3f));
      }
      else if (charcode < 0xd800 || charcode >= 0xe000) {
        utf8.push(0xe0 | (charcode >> 12), 
        0x80 | ((charcode>>6) & 0x3f), 
        0x80 | (charcode & 0x3f));
      }
      // surrogate pair
      else {
        i++;
        // UTF-16 encodes 0x10000-0x10FFFF by
        // subtracting 0x10000 and splitting the
        // 20 bits of 0x0-0xFFFFF into two halves
        charcode = 0x10000 + (((charcode & 0x3ff)<<10)
        | (str.charCodeAt(i) & 0x3ff));
        utf8.push(0xf0 | (charcode >>18), 
        0x80 | ((charcode>>12) & 0x3f), 
        0x80 | ((charcode>>6) & 0x3f), 
        0x80 | (charcode & 0x3f));
      }
    }
    return utf8;
  }

  function Blob(chunks, opts) {
    for (var i = 0, len = chunks.length; i < len; i++) {
      var chunk = chunks[i]
      chunks[i] = 
        chunk instanceof Blob ? chunk._buffer :
        typeof chunk === 'string' ? toUTF8Array(chunk) : chunk
    }

    this._buffer = [].concat.apply([], chunks)
    this.size = this._buffer.length
    this.type = opts ? opts.type || '' : ''
  }

  Blob.prototype.slice = function(start, end, type) {
    var slice = this._buffer.slice(start || 0, end || this._buffer.length)
    return new Blob([slice], type || '')
  }

  Blob.prototype.toString = function() {
    return '[object Blob]'
  }

  if (typeof Symbol !== 'undefined') {
    Blob.prototype[Symbol.toStringTag] = 'Blob'
  }

  return Blob
}

module.exports = (function() {
  if (blobSupported) {
    return blobSupportsArrayBufferView ? global.Blob : BlobConstructor;
  } else if (blobBuilderSupported) {
    return BlobBuilderConstructor;
  } else {
    return FakeBlobBuilder();
  }
})();