--- /dev/null
+'use strict';
+module.exports = function (url) {
+ if (typeof url !== 'string') {
+ throw new TypeError('Expected a string');
+ }
+
+ url = url.trim();
+
+ if (/^\.*\//.test(url)) {
+ return url;
+ }
+
+ return url.replace(/^(?!(?:\w+:)?\/\/)/, 'http://');
+};