javascript: photoshop save for web

gistfile1

function saveForWebPNG(outputFolderStr, filename)
{
    var opts, file;
    opts = new ExportOptionsSaveForWeb();
    opts.format = SaveDocumentType.PNG;
    opts.PNG8 = false;
    opts.quality = 100;
    if (filename.length > 27) {
        file = new File(outputFolderStr + "/temp.png");
        activeDocument.exportDocument(file, ExportType.SAVEFORWEB, opts);
        file.rename(filename + ".png");
    }
    else {
        file = new File(outputFolderStr + "/" + filename + ".png");
        activeDocument.exportDocument(file, ExportType.SAVEFORWEB, opts);
    }
    //Photoshop on Mac limits the length of a File object's file name to 31 characters. 
}