test.html

<script>
function errorHandler(e) {
  var msg = '';

  switch (e.code) {
    case FileError.QUOTA_EXCEEDED_ERR:
      msg = 'QUOTA_EXCEEDED_ERR';
      break;
    case FileError.NOT_FOUND_ERR:
      msg = 'NOT_FOUND_ERR';
      break;
    case FileError.SECURITY_ERR:
      msg = 'SECURITY_ERR';
      break;
    case FileError.INVALID_MODIFICATION_ERR:
      msg = 'INVALID_MODIFICATION_ERR';
      break;
    case FileError.INVALID_STATE_ERR:
      msg = 'INVALID_STATE_ERR';
      break;
    default:
      msg = 'Unknown Error';
      break;
  };

  console.log('Error: ' + msg);
}


window.requestFileSystem  = window.requestFileSystem || window.webkitRequestFileSystem;
//window.requestFileSystem(window.TEMPORARY, 5*1024*1024 /*5MB*/, onInitFs, errorHandler);


var requestedBytes = 1024*1024; 

navigator.webkitPersistentStorage.requestQuota (
    requestedBytes, function(grantedBytes) {
				console.log('we were granted ', grantedBytes, 'bytes');  
        window.webkitRequestFileSystem(PERSISTENT, grantedBytes, onInitFs, errorHandler); 

    }, function(e) { console.log('Error', e); }
);

function onInitFs(fs) {

  fs.root.getFile('log.txt', {create: true}, function(fileEntry) {

    // Create a FileWriter object for our FileEntry (log.txt).
    fileEntry.createWriter(function(fileWriter) {

      fileWriter.onwriteend = function(e) {
        console.log('Write completed.');
      };

      fileWriter.onerror = function(e) {
        console.log('Write failed: ' + e.toString());
      };

      // Create a new Blob and write it to log.txt.
      var blob = new Blob(['Lorem Ipsum'], {type: 'text/plain'});

      fileWriter.write(blob);

    }, errorHandler);

  }, errorHandler);

}



</script>