Intelligently buils an URL from the arguments.

url-builder.js

/**
 * NOTE: Requires Underscore >=1.4.3
 * 
 * Intelligently buils an URL from the arguments.
 *     . If the parameter is a string or a number, is part or the URL (in the order passed)
 *     . If the parameter is an object, is taken as a query param.
 *
 * Examples:
 *     urlBuilder('http://google.com')
 *         'http://google.com'
 * 
 *     urlBuilder('http://myrestapi.com', 'users')
 *         'http://myrestapi.com/users'
 * 
 *     urlBuilder('http://myrestapi.com', 'user', userId, 'posts')
 *         'http://myrestapi.com/user/{userId}/posts'
 * 
 *     urlBuilder('http://myrestapi.com', 'user', userId, 'posts', {page: 2, limit:10})
 *         'http://myrestapi.com/user/{userId}/posts?page=2&limit=10'
 * 
 * @return {string} The formed URL.
 */
function urlBuilder() {
    var argsArr = Array.prototype.slice.call(arguments);

    var args = _.groupBy(argsArr, function(arg) {
        if (_.isString(arg) || _.isNumber(arg)) {
            return 'paths';
        }

        if (_.isObject(arg)) {
            return 'params';
        }
    });

    // error: no path passed
    if (_.size(args.paths) === 0) {
        return '';
    }

    // replace double slashes without loosing '://'
    var exp = new RegExp('([^:])//'),
        url = args.paths.join('/').replace(exp, '$1/');

    if (!_.isEmpty(args.params)) {
        // build the query string
        url += '?' + _.map(_.extend.apply(_, _.union([{}], args.params)), function(value, key) {
            return key + '=' + value;
        }).join('&');
    }

    return url;
}