gistfile1.js

function formatFileError(err){
  var sb = err.toString();
	for( var k in err ){
		sb += "\n "+k+"="+err[k];
		if( k == "code" ){
			sb+=" ";
			switch (err[k]) {
			case FileError.QUOTA_EXCEEDED_ERR: sb += 'QUOTA_EXCEEDED_ERR'; break;
			case FileError.NOT_FOUND_ERR: sb += 'NOT_FOUND_ERR'; break;
			case FileError.SECURITY_ERR: sb += 'SECURITY_ERR'; break;
			case FileError.INVALID_MODIFICATION_ERR: sb += 'INVALID_MODIFICATION_ERR'; break;
			case FileError.INVALID_STATE_ERR: sb += 'INVALID_STATE_ERR'; break;
			};
		}
	}
	return sb;
}

function testFileSave(){
	try{
		var save_file = "file1";
		var save_data = JSON.stringify({ key1: 'v1',key2: 'v2',key3: 'v3'}); 
		// PERSISTENT or TEMPORARY 
		window.storageInfo.requestQuota(window.PERSISTENT, 8 * 1024 * 1024, function(granted_bytes){
			try{
				if(! window.requestFileSystem ){
					window.requestFileSystem = window.webkitRequestFileSystem;
				}
				window.requestFileSystem( window.PERSISTENT, granted_bytes, function(fs){
					try{
						fs.root.getFile( save_file, {create: true }, function(entry){
							// entry.isFile // entry.name // entry.fullPath 
							try{
								entry.createWriter(function(writer) {
									try{
										writer.onwriteend = function(e) {
											console.log('Write completed.');
										};
										writer.onerror = function(e) {
											console.log("write error:"+ formatFileError(err) );
										};
										var bb = new BlobBuilder(); // Note: window.WebKitBlobBuilder in Chrome 12.
										bb.append(save_data);
										writer.write(bb.getBlob('text/plain'));
									}catch(exc){
										console.log("write exception:"+formatFileError(exc));
									}
								},function(err){
									console.log("createWriter failed."+formatFileError(err));
								});
							}catch(exc){
								console.log("createWriter exception:"+formatFileError(exc));
							}
						},function(err){
							console.log("getFile failed."+formatFileError(err));
						});
					}catch(exc){
						console.log("getFile exception:"+formatFileError(exc));
					}
				},function(err){
					console.log("requestFileSystem failed."+formatFileError(err));
				});
			}catch( exc ){
				console.log("requestFileSystem exception:"+formatFileError(exc));
			}
		},function(err){
			console.log("requestQuota failed."+formatFileError(err));
		});
	}catch(exc){
		console.log("requestQuota exception:"+formatFileError(exc));
	}
}