查看一個簡單的jQuery的例子來遍歷一個JavaScript數組對象。

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. ];
9. $.each(json, function(idx, obj) {
10. alert(obj.tagName);
11. });

上面的代碼片斷工作正常，提示 “apple”, “orange” … 等，如預期一樣。
問題: JSON 字符串

下面的例子中，聲明了一個JSON字符串（隨附單或雙引號）直接地。

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"
   }]‘;
5. $.each(json, function(idx, obj) {
6. alert(obj.tagName);
7. });

在Chrome中，它顯示在控制臺下面的錯誤：

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

解決方案：JSON字符串轉換為JavaScript對象。
要修復它，通過標準JSON.parse()或jQuery 的 $.parseJSON 將其轉換為JavaScript對象。

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"}]‘;
5. $.each(JSON.parse(json), function(idx, obj) {
6. alert(obj.tagName);
7. });
9. //or
11. $.each($.parseJSON(json), function(idx, obj) {
12. alert(obj.tagName);
13. });

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