JQuery中extend的用法

jQuery.extend = jQuery.fn.extend = function() ...{
    var options, name, src, copy, copyIsArray, clone,
        target = arguments[0] || ...{},//参数目标对象
        i = 1,
        length = arguments.length,//参数长度
        deep = false;//是否为深度复制

    // Handle a deep copy situation
    //如果为深度复制,则目标对象和原对象游标值i，以及深度值都进行更新
    if ( typeof target === "boolean" ) ...{
        deep = target;
        target = arguments[1] || ...{};
        // skip the boolean and the target
        i = 2;
    }

    // Handle case when target is a string or something (possible in deep copy)
    //当目标对象的值类型错误，则重置为{}
    if ( typeof target !== "object" && !jQuery.isFunction(target) ) ...{
        target = ...{};
    }

    // extend jQuery itself if only one argument is passed
    //当参数值长度为1的情况下，目标对象就为jQuery自身
    if ( length === i ) ...{
        target = this;
        --i;
    }

    for ( ; i < length; i++ ) ...{
        // Only deal with non-null/undefined values
        if ( (options = arguments[ i ]) != null ) ...{//忽略空对象
            // Extend the base object
            for ( name in options ) ...{
                src = target[ name ];
                copy = options[ name ];//存储对象的值

                // Prevent never-ending loop
                if ( target === copy ) ...{
                    continue;
                }

                // Recurse if we're merging plain objects or arrays
                  //深度复制只有属性深度多于俩层的对象关系的结构的，如{a:{s:21,age:11}}或{a:['s'=>21,'age'=>11]}
                if ( deep && copy && ( jQuery.isPlainObject(copy) || (copyIsArray = jQuery.isArray(copy)) ) ) ...{
                    if ( copyIsArray ) ...{//如果是数组对象
                        copyIsArray = false;
                        clone = src && jQuery.isArray(src) ? src : [];

                    } else ...{//普通对象
                        clone = src && jQuery.isPlainObject(src) ? src : ...{};
                    }

                    // Never move original objects, clone them
                    // 调用自身进行递归复制
                    target[ name ] = jQuery.extend( deep, clone, copy );

                // Don't bring in undefined values
                } else if ( copy !== undefined ) ...{//非深度CP直接覆盖目标属性
                    target[ name ] = copy;
                }
            }
        }
    }

    // Return the modified object
    return target;
};