_filename = function (config, dt) {
	// Backwards compatibility
	var filename =
		config.filename === '*' &&
		config.title !== '*' &&
		config.title !== undefined &&
		config.title !== null &&
		config.title !== ''
			? config.title
			: config.filename;

	if (typeof filename === 'function') {
		filename = filename(config, dt);
	}

	if (filename === undefined || filename === null) {
		return null;
	}

	if (filename.indexOf('*') !== -1) {
		filename = filename.replace('*', $('head > title').text()).trim();
	}

	// Strip characters which the OS will object to
	filename = filename.replace(/[^a-zA-Z0-9_\u00A1-\uFFFF\.,\-_ !\(\)]/g, '');

	var extension = _stringOrFunction(config.extension, config, dt);
	if (!extension) {
		extension = '';
	}

	return filename + extension;
}
Get the file name for an exported file.

@param {object} config Button configuration
@param {object} dt DataTable instance