/**
 * 拓展对象
 */
exports.extend = function extend(target) {
    var sources = Array.prototype.slice.call(arguments, 1);

    for (var i = 0; i < sources.length; i += 1) {
        var source = sources[i];
        for (var key in source) {
            if (source.hasOwnProperty(key)) {
                target[key] = source[key];
            }
        }
    }

    return target;
};