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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);
});