gistfile1.js

// Source: http://davidflanagan.com/Talks/jsconf11/BytesAndBlobs.html

// Load File
function loadBlob(path, callback) {
  webkitRequestFileSystem( // Ask for filesystem
    PERSISTENT, 50*1024*1024, 
    function(fs) { // When we get filesystem
      fs.root.getFile( // Ask for a fs entry
        path, {},      // With this name
        function(entry) {  // When we get entry
          entry.file(      // Ask for the file
            function(f) {  // When we get file
              callback(f); // Pass to callback
            });
        });
    });
}

// Save File
function saveBlob(blob, path, done) {
  webkitRequestFileSystem( // Ask for fs
    PERSISTENT,     // Save across sessions
    50*1024*1024,   // Allow 50Mb 
    function(fs) {  // When we get the fs
      fs.root.getFile( // Ask for a fs entry
        path,          // With specified path
        {create:true}, // Create if needed.
        function(entry) { // When we get entry
          entry.createWriter( // Ask for a writer
            function(writer) { // When we get writer
              writer.write(blob); // Write blob
              writer.onwrite = done;
            });
        });
    });
}