合并对象

var isObject = function(obj) {
    return obj !== null && typeof obj === 'object' && Object.getPrototypeOf(obj) === Object.prototype;
};
var extend = function(target, obj) {
    for (var param in obj) {
        var src = target[param];
        var copy = obj[param];
        if (src === copy) {
            continue;
        }
        if (isObject(copy)) {
            src = src || {};
            target[param] = extend(src, copy);
        } else {
            target[param] = copy;
        }
    }
    return target;
};