js 中 字符串转换为json数组

字符串转换为json数组
　<script type="text/javascript">
　　var str = '[ {"green":10,"size":5,"strock":12},{"green":10,"size":2,"strock":20} ]';
　　var json = eval(str); 
      out.print("{'is_OK':true,'message':'"+str+"'}") 
　</script>