JQuery $.each遍历JSON字符串报Uncaught TypeError:Cannot use 'in' operator to search for

查看一个简单的jQuery的例子来遍历一个JavaScript数组对象。

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1. var json = [
2. {"id":"1","tagName":"apple"},
3. {"id":"2","tagName":"orange"},
4. {"id":"3","tagName":"banana"},
5. {"id":"4","tagName":"watermelon"},
6. {"id":"5","tagName":"pineapple"}
7. ];
8. $.each(json, function(idx, obj) {
9. alert(obj.tagName);
10. });

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。

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1. var json = '[{"id":"1","tagName":"apple"},{"id":"2","tagName":"orange"},
2. {"id":"3","tagName":"banana"},{"id":"4","tagName":"watermelon"},
3. {"id":"5","tagName":"pineapple"}]';
4. $.each(json, function(idx, obj) {
5. alert(obj.tagName);
6. });

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。

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1. var json = '[{"id":"1","tagName":"apple"},{"id":"2","tagName":"orange"},
2. {"id":"3","tagName":"banana"},{"id":"4","tagName":"watermelon"},
3. {"id":"5","tagName":"pineapple"}]';
4. $.each(JSON.parse(json), function(idx, obj) {
5. alert(obj.tagName);
6. });
7. //or
8. $.each($.parseJSON(json), function(idx, obj) {
9. alert(obj.tagName);
10. });