ajax请求成功返回数据，转成数组后，for遍历取不到值的有关问题
ajax请求成功返回数据，转成数组后，for遍历取不到值的问题？
如题，ajax请求成功后返回了数据，转数组如图：
alert（arr.length）出数据长度为8。但是接下来通过for遍历取值时却无法取到值，取出的值是undefined！求解，求解，求解！！！
返回的数据如下：
[{"newid":"1189","newimg":"http://xiangfit.com/Web/ueditor/ueditornet/net/upload/2012-09-02-24dc2d2125-53ba-495f-b685-cfa1017a1dc9.png","newtitle":"2014/7/4 0:00:00","newspartinfo":"人们对下腹肌的训练关注程度少之又少，缘由小腹肌涉及的范围实在少之又少。但为了追求更完美的腹肌效果，下面介绍下腹的入门训练","newclick":"0","newtype":"照片0","newtime":"2014/7/3 15:29:11","userid":"3","NewsAudi":"True","NewsTag":"强大的腹肌需要不断的突破。"}],[{"newid":"1190","newimg":"http://xiangfit.com/Web/ueditor/ueditornet/net/upload/2012-09-02-087699772b-0fa5-454f-b8b9-b57d8edbde72.png","newtitle":"2014/7/3 0:00:00","newspartinfo":"增强腹肌的方法有很多种，但不是所有的动作都适合您。如仰卧起坐适合新手，对腹肌较强者效果并非很好。下面介绍的动作算是腹肌训","newclick":"0","newtype":"照片0","newtime":"2014/7/3 15:51:48","userid":"3","NewsAudi":"True","NewsTag":""}],[{"newid":"1105","newimg":"Sources/Image/treetime/201441113512231.png","newtitle":"2012/9/8 0:00:00","newspartinfo":"∮∫∮穿正装的样子，正所谓有身材穿什么都好看，哈哈。sdfsdfsd","newclick":"1","newtype":"照片1","newtime":"2014/4/11 13:51:01","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}],[{"newid":"1151","newimg":"/Web/ueditor/ueditornet/net/upload/2012-09-02-375062245c-f3b5-42bc-9e19-893bef30b074.png","newtitle":"2012/9/8 0:00:00","newspartinfo":"∮∫∮穿正装的样子，正所谓有身材穿什么都好看，哈哈","newclick":"0","newtype":"照片0","newtime":"2014/6/3 16:23:39","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}],[{"newid":"1152","newimg":"/../Web/ueditor/ueditornet/net/upload/2012-09-26-0406b6ba22-cf41-41a1-8684-b7bb17af35fb.png","newtitle":"2012/9/8 0:00:00","newspartinfo":"滞空是篮球运动员的一项技术动作，是指运动员跳起离地之后在空中平稳飞行好像停滞在空中。而我们知道滞空时间的长短取决身体的协","newclick":"0","newtype":"照片0","newtime":"2014/6/3 16:24:31","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}],[{"newid":"1153","newimg":"Sources/Image/treetime/20144110364812.jpg","newtitle":"2012/9/8 0:00:00","newspartinfo":"没有什么比户外跑更能消除您多余的脂肪了！穿上跑鞋、挂上耳机，然后把减肥这件大事交给跑步吧！","newclick":"0","newtype":"照片0","newtime":"2014/6/3 16:24:53","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}],[{"newid":"1154","newimg":"/../Web/ueditor/ueditornet/net/upload/2012-09-25-38275a838d-960a-48e4-a09e-817c9f83affe.png","newtitle":"2012/9/8 0:00:00","newspartinfo":"大家首先得弄清大腿和小腿在弹跳上的作用区别。总的来说大腿力量足的人跳的高，小腿力量强的弹速快。而这里主要为大家介绍增快弹","newclick":"0","newtype":"照片0","newtime":"2014/6/3 16:27:10","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}],[{"newid":"1159","newimg":"/Web/ueditor/ueditornet/net/upload/2012-09-01-32ed0fb40b-4a44-4024-a01c-e031fdf79317.png","newtitle":"2012/9/8 0:00:00","newspartinfo":"性感发达的背阔肌能不仅能为男人增添魅力，更重要的是背阔肌起到保护脊柱的作用，使其更有能力去抵抗各类脊柱引起的疾病。","newclick":"0","newtype":"照片0","newtime":"2014/6/4 16:46:16","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}]
弄了一下午也不知道是怎么回事，希望大神们指点下，谢谢。
------解决方案--------------------
arr=eval(mes);
for(var i in arr){
alert(arr[i]["newid"]);
}
如题，ajax请求成功后返回了数据，转数组如图：
alert（arr.length）出数据长度为8。但是接下来通过for遍历取值时却无法取到值，取出的值是undefined！求解，求解，求解！！！
返回的数据如下：
[{"newid":"1189","newimg":"http://xiangfit.com/Web/ueditor/ueditornet/net/upload/2012-09-02-24dc2d2125-53ba-495f-b685-cfa1017a1dc9.png","newtitle":"2014/7/4 0:00:00","newspartinfo":"人们对下腹肌的训练关注程度少之又少，缘由小腹肌涉及的范围实在少之又少。但为了追求更完美的腹肌效果，下面介绍下腹的入门训练","newclick":"0","newtype":"照片0","newtime":"2014/7/3 15:29:11","userid":"3","NewsAudi":"True","NewsTag":"强大的腹肌需要不断的突破。"}],[{"newid":"1190","newimg":"http://xiangfit.com/Web/ueditor/ueditornet/net/upload/2012-09-02-087699772b-0fa5-454f-b8b9-b57d8edbde72.png","newtitle":"2014/7/3 0:00:00","newspartinfo":"增强腹肌的方法有很多种，但不是所有的动作都适合您。如仰卧起坐适合新手，对腹肌较强者效果并非很好。下面介绍的动作算是腹肌训","newclick":"0","newtype":"照片0","newtime":"2014/7/3 15:51:48","userid":"3","NewsAudi":"True","NewsTag":""}],[{"newid":"1105","newimg":"Sources/Image/treetime/201441113512231.png","newtitle":"2012/9/8 0:00:00","newspartinfo":"∮∫∮穿正装的样子，正所谓有身材穿什么都好看，哈哈。sdfsdfsd","newclick":"1","newtype":"照片1","newtime":"2014/4/11 13:51:01","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}],[{"newid":"1151","newimg":"/Web/ueditor/ueditornet/net/upload/2012-09-02-375062245c-f3b5-42bc-9e19-893bef30b074.png","newtitle":"2012/9/8 0:00:00","newspartinfo":"∮∫∮穿正装的样子，正所谓有身材穿什么都好看，哈哈","newclick":"0","newtype":"照片0","newtime":"2014/6/3 16:23:39","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}],[{"newid":"1152","newimg":"/../Web/ueditor/ueditornet/net/upload/2012-09-26-0406b6ba22-cf41-41a1-8684-b7bb17af35fb.png","newtitle":"2012/9/8 0:00:00","newspartinfo":"滞空是篮球运动员的一项技术动作，是指运动员跳起离地之后在空中平稳飞行好像停滞在空中。而我们知道滞空时间的长短取决身体的协","newclick":"0","newtype":"照片0","newtime":"2014/6/3 16:24:31","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}],[{"newid":"1153","newimg":"Sources/Image/treetime/20144110364812.jpg","newtitle":"2012/9/8 0:00:00","newspartinfo":"没有什么比户外跑更能消除您多余的脂肪了！穿上跑鞋、挂上耳机，然后把减肥这件大事交给跑步吧！","newclick":"0","newtype":"照片0","newtime":"2014/6/3 16:24:53","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}],[{"newid":"1154","newimg":"/../Web/ueditor/ueditornet/net/upload/2012-09-25-38275a838d-960a-48e4-a09e-817c9f83affe.png","newtitle":"2012/9/8 0:00:00","newspartinfo":"大家首先得弄清大腿和小腿在弹跳上的作用区别。总的来说大腿力量足的人跳的高，小腿力量强的弹速快。而这里主要为大家介绍增快弹","newclick":"0","newtype":"照片0","newtime":"2014/6/3 16:27:10","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}],[{"newid":"1159","newimg":"/Web/ueditor/ueditornet/net/upload/2012-09-01-32ed0fb40b-4a44-4024-a01c-e031fdf79317.png","newtitle":"2012/9/8 0:00:00","newspartinfo":"性感发达的背阔肌能不仅能为男人增添魅力，更重要的是背阔肌起到保护脊柱的作用，使其更有能力去抵抗各类脊柱引起的疾病。","newclick":"0","newtype":"照片0","newtime":"2014/6/4 16:46:16","userid":"3","NewsAudi":"False","NewsTag":"身材好，即使穿西装也很迷人！"}]
弄了一下午也不知道是怎么回事，希望大神们指点下，谢谢。
------解决方案--------------------
arr=eval(mes);
for(var i in arr){
alert(arr[i]["newid"]);
}