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);});