jqueryextend解析

1.jquery支持和深度拷贝和浅度拷贝
2.第一个参数是true就是深度拷贝
3.深度拷贝主要实现的时候数组和对象的深度考虑
4.如果不深度拷贝数组和对象里面的内容也会改变

jQuery.extend = jQuery.fn.extend = function() {
    var options, name, src, copy, copyIsArray, clone,
        target = arguments[ 0 ] || {},
        i = 1,
        length = arguments.length,
        deep = false;

    // Handle a deep copy situation
    if ( typeof target === "boolean" ) {
        deep = target;

        // Skip the boolean and the target
        target = arguments[ i ] || {};
        i++;
    }

    // Handle case when target is a string or something (possible in deep copy)
    if ( typeof target !== "object" && !jQuery.isFunction( target ) ) {
        target = {};
    }

    // Extend jQuery itself if only one argument is passed
    if ( i === length ) {
        target = this;
        i--;
    }

    for ( ; i < length; i++ ) {

        // Only deal with non-null/undefined values
        if ( ( options = arguments[ i ] ) != null ) {

            // Extend the base object
            for ( name in options ) {
                src = target[ name ];
                copy = options[ name ];

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

                // Recurse if we're merging plain objects or arrays
                //判断是否为数组和对象
                if ( deep && copy && ( jQuery.isPlainObject( copy ) ||
                    ( copyIsArray = Array.isArray( copy ) ) ) ) {

                    if ( copyIsArray ) {//是否数组
                        copyIsArray = false;
                        clone = src && Array.isArray( src ) ? src : [];

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

                    // Never move original objects, clone them 递归
                    target[ name ] = jQuery.extend( deep, clone, copy );

                // Don't bring in undefined values
                } else if ( copy !== undefined ) {
                    target[ name ] = copy;
                }
            }
        }
    }

    // Return the modified object
    return target;
};

这个继承的话我个人觉得会有一定的问题，如果遍历的太多，会不会造成栈太深，使用非递归的方法改进下