'use strict';
module.exports = function (url) {
    if (typeof url !== 'string') {
        throw new TypeError('Expected a string, got ' + typeof url);
    }

    url = url.trim();

    if (/^\.*\/|^(?!localhost)\w+:/.test(url)) {
        return url;
    }

    return url.replace(/^(?!(?:\w+:)?\/\/)/, 'http://');
};
