How to read/write local files through a web page?

Question

I am writing a html based app, and want to store and retrieve data from local file. This app will not be hosted on a web server.

Can anyone please help enlighten the

Answer 1

The answer to this question depends on your answers to the following questions:

• Are you fine with the fact that support for writing files currently exists only in Chromium-based browsers (Chrome & Opera)?
• Are you fine with utilizing an as-of-now proprietary API to take advantage of such a capbility?
• Are you fine with the possibility of removal of said API in the future?
• Are you fine with the constriction of files created with said API to a sandbox (a location outside of which the files can produce no effect) on disk?
• Are you fine with the use of a virtual file system (a directory structure which does not necessarily exist on disk in the same form that it does when accessed from within the browser) to represent such files?

If you answered "yes" to all of the above, then with the File, FileWriter and FileSystem APIs, you can write files from the context of a browser tab/window using Javascript.

How, you asked?

BakedGoods*

Write file:

bakedGoods.set({
    data: [{key: "testFile", value: "Hello world!", dataFormat: "text/plain"}],
    storageTypes: ["fileSystem"],
    options: {fileSystem:{storageType: Window.PERSISTENT}},
    complete: function(byStorageTypeStoredItemRangeDataObj, byStorageTypeErrorObj){}
});

Read file:

bakedGoods.get({
        data: ["testFile"],
        storageTypes: ["fileSystem"],
        options: {fileSystem:{storageType: Window.PERSISTENT}},
        complete: function(resultDataObj, byStorageTypeErrorObj){}
});

Using the raw File, FileWriter, and FileSystem APIs

Write file:

function onQuotaRequestSuccess(grantedQuota)
{

    function saveFile(directoryEntry)
    {

        function createFileWriter(fileEntry)
        {

            function write(fileWriter)
            {
                var dataBlob = new Blob(["Hello world!"], {type: "text/plain"});
                fileWriter.write(dataBlob);              
            }

            fileEntry.createWriter(write);
        }

        directoryEntry.getFile(
            "testFile", 
            {create: true, exclusive: true},
            createFileWriter
        );
    }

    requestFileSystem(Window.PERSISTENT, grantedQuota, saveFile);
}

var desiredQuota = 1024 * 1024 * 1024;
var quotaManagementObj = navigator.webkitPersistentStorage;
quotaManagementObj.requestQuota(desiredQuota, onQuotaRequestSuccess);

Read file:

function onQuotaRequestSuccess(grantedQuota)
{

    function getfile(directoryEntry)
    {

        function readFile(fileEntry)
        {

            function read(file)
            {
                var fileReader = new FileReader();

                fileReader.onload = function(){var fileData = fileReader.result};
                fileReader.readAsText(file);             
            }

            fileEntry.file(read);
        }

        directoryEntry.getFile(
            "testFile", 
            {create: false},
            readFile
        );
    }

    requestFileSystem(Window.PERSISTENT, grantedQuota, getFile);
}

var desiredQuota = 1024 * 1024 * 1024;
var quotaManagementObj = navigator.webkitPersistentStorage;
quotaManagementObj.requestQuota(desiredQuota, onQuotaRequestSuccess);

---

But what if you answered "no" to any of the questions at the beginning?

If you are open to non-native solutions, Silverlight also allows for file i/o from a tab/window contest through IsolatedStorage. However, managed code is required to utilize this facility; a solution which requires writing such code is beyond the scope of this question.

Of course, a solution which makes use of complementary managed code, leaving one with only Javascript to write, is well within the scope of this question ;) :

//Write file to first of either FileSystem or IsolatedStorage
bakedGoods.set({
    data: [{key: "testFile", value: "Hello world!", dataFormat: "text/plain"}],
    storageTypes: ["fileSystem", "silverlight"],
    options: {fileSystem:{storageType: Window.PERSISTENT}},
    complete: function(byStorageTypeStoredItemRangeDataObj, byStorageTypeErrorObj){}
});

*BakedGoods is maintained by none other than this guy right here :)