Create and write data to a file

I’m developping an application for mapping…
I created KML and JSON string and I need to store them in files in phones memory, to do so, I used the following code :

>  var fileObject;

>   document.addEventListener("deviceready", onDeviceReady, true);
>   
>   function onDeviceReady() 
>   {
>     window.requestFileSystem(LocalFileSystem.PERSISTENT, 0,onFileSystemSuccess, fail);
>   }

>   function onFileSystemSuccess(fileSystem) {
>     fileSystem.root.getFile("readme.txt",{create: true, exclusive: false},gotFileEntry, fail);
>   }

>   function gotFileEntry(fileEntry) {
>     fileObject = fileEntry;
>     $('#saveFile_btn').on('click', function() {
>       saveFileContent();
>     });
>   }

>   function saveFileContent() {
>     fileObject.createWriter(gotFileWriter, fail);
>   }

>   function gotFileWriter(writer) {
>     var myText = document.getElementById('my_text').value;
>     writer.write(myText);
>     writer.onwriteend = function(evt) {
>       $('#message').html('<p>File contents have been written.<br /><strong>File path:</strong> ' + fileObject.fullPath + '</p>');
>       var reader = new FileReader();
>       reader.readAsText(fileObject);
>       reader.onload = function(evt) {
>         $('#contents').html('<strong>File contents:</strong> <br />'+ evt.target.result);
>       };
>     };
>   }

>   function fail(error){
>     alert(error.code);
>   }

the result was not an error, but I can’t find the file in the memory.