jquery遍历json对象数组，报错

查看一个简单的jQuery的例子来遍历一个JavaScript数组对象。

var json = [  
{"id":"1","tagName":"apple"},  
{"id":"2","tagName":"orange"},  
{"id":"3","tagName":"banana"},  
{"id":"4","tagName":"watermelon"},  
{"id":"5","tagName":"pineapple"}  
];  
  
$.each(json, function(idx, obj) {  
alert(obj.tagName);  
});  

上面的代码片断工作正常，提示 “apple”, “orange” … 等，如预期一样。
问题: JSON 字符串

下面的例子中，声明了一个JSON字符串（随附单或双引号）直接地。

var json = '[{"id":"1","tagName":"apple"},{"id":"2","tagName":"orange"},  
{"id":"3","tagName":"banana"},{"id":"4","tagName":"watermelon"},  
{"id":"5","tagName":"pineapple"}]';  
  
$.each(json, function(idx, obj) {  
alert(obj.tagName);  
});  

　　

在Chrome中，它显示在控制台下面的错误：

Uncaught TypeError: Cannot use 'in' operator to search for '156' 
in [{"id":"1","tagName":"apple"}...

解决方案：JSON字符串转换为JavaScript对象。
要修复它，通过标准JSON.parse()或jQuery 的 $.parseJSON 将其转换为JavaScript对象。

var json = '[{"id":"1","tagName":"apple"},{"id":"2","tagName":"orange"},  
{"id":"3","tagName":"banana"},{"id":"4","tagName":"watermelon"},  
{"id":"5","tagName":"pineapple"}]';  
  
$.each(JSON.parse(json), function(idx, obj) {  
alert(obj.tagName);  
});  
  
//or   
  
$.each($.parseJSON(json), function(idx, obj) {  
alert(obj.tagName);  
});