--- /dev/null
+/* @flow */
+"use strict";
+
+/**
+ * Check if a string is a single line (i.e. does not contain
+ * any newline characters).
+ *
+ * @param {string} input
+ * @return {boolean}
+ */
+module.exports = function(input /*: string*/) /*: boolean*/ {
+ return !/[\n\r]/.test(input);
+};