App crashed with file function

window.requestFileSystem = window.requestFileSystem || window.webkitRequestFileSystem;
window.LocalFileSystem = window.LocalFileSystem || {PERSISTENT: window.PERSISTENT};

window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, gotFS, fail);
function gotFS(fileSystem) {
    fileSystem.root.getDirectory("DO_NOT_DELETE", 
        {create: true, exclusive: false}, 
        gotDirEntry, 
        fail);
}
function gotDirEntry(dirEntry) {
    dir = dirEntry;
    dirEntry.getFile("sample.json", 
        {create: false, exclusive: false}, 
        readSuccess, 
        fileDonotexist);
}
function fileDonotexist(dirEntry) {
    dir.getFile("sample.json", 
        {create: true, exclusive: false}, 
        gotFileEntry, 
        fail);
}
function gotFileEntry(fileEntryWrite) {
    fileEntryWrite.createWriter(gotFileWriter, fail);
}
function gotFileWriter(writer) {
    writer.onerror = function(evt) {
    };
    writer.write(localData);
    writer.onwriteend = function(evt) {
        dir.getFile("sample.json", 
            {create: false, exclusive: false}, 
            readSuccess, 
            fail);
    };
}
function readSuccess(fileE) {
    fileE.file(readAsText, fail);
}
function fail(error) {
    alert("fail");
}
function readAsText(readerDummy) {
    var reader = new FileReader();

    reader.onloadstart = function(evt) {};
    reader.onprogress = function(evt) {};
    reader.onerror = function(evt) {};

    reader.onloadend = function(evt) {
        console.log("read success");
    };
    reader.readAsText(readerDummy);
}