function downloadFile(fileName, content){

    var aLink = document.createElement('a');

    var blob = new Blob([content]);

    var evt = document.createEvent("HTMLEvents");

    // initEvent 不加后两个参数在FF下会报错, 感谢 Barret Lee 的反馈

    evt.initEvent("click", false, false);

    aLink.download = fileName;

    aLink.href = URL.createObjectURL(blob);

    aLink.dispatchEvent(evt);

}