jQuery1.6 jQuery.extend

jQuery.extend = jQuery.fn.extend = function() {
	var options, name, src, copy, copyIsArray, clone,
		target = arguments[0] || {},
		i = 1,
		length = arguments.length,
		deep = false;
	if ( typeof target === "boolean" ) {//深度复制
		deep = target;
		target = arguments[1] || {};
		i = 2;
	}
	if ( typeof target !== "object" && !jQuery.isFunction(target) ) {目标对象的类型不是"object"或者"function"
		target = {};
	}
	if ( length === i ) {//如果只有一个参数传递，扩展jQuery的本身，
		target = this;
		--i;
	}
	for ( ; i < length; i++ ) {
		if ( (options = arguments[ i ]) != null ) {//只处理非空的值
			for ( name in options ) {
				src = target[ name ];
				copy = options[ name ];
				if ( target === copy ) {//防止死循环a{} b{x:a} $.extend(a,b);
					continue;
				}
				if ( deep && copy && ( jQuery.isPlainObject(copy) || (copyIsArray = jQuery.isArray(copy)) ) ) {//合并

　　　　　　　　　　　　　　//处理深度复制，如果copy存在，并且是纯对象或者数组
					if ( copyIsArray ) {
						copyIsArray = false;
						clone = src && jQuery.isArray(src) ? src : [];
					} else {
						clone = src && jQuery.isPlainObject(src) ? src : {};
					}
					//进行递归
					target[ name ] = jQuery.extend( deep, clone, copy );
				} else if ( copy !== undefined ) {
					target[ name ] = copy;//直接复制
				}
			}
		}
	}
	return target;//返回目标对象
};

例：

var a={"height":1,"width":12,"location":{"X":2}};

var b={"height":2,"width":12,"location":{"x":1,"y":1}};

$.extend(a,b);//a={"height":2,"width":12,"location":{"x":1,"y":1}};

$.extend(true,a,b)//深度复制a={"height":2,"width":12,"location":{"X":2,"x":1,"y":1}};

$.extend{a}//扩展$自身