jquery each报 Uncaught TypeError: Cannot use 'in' operator to search for错误

在写前端的时候用jquery来遍历后台传来的json数组时候遇到这个错误：Uncaught TypeError: Cannot use 'in' operator to search for。后来查到原因是因为：一部分浏览器后端传过来的是json对象，但是我们前端是需要Javascript的对象，所以需要做个转换JSON.parse() or jQuery $.parseJSON

Review a simple jQuery example to loop over a JavaScript array object.

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);
});

Above code snippet is working fine, prompts the “apple”, “orange” … as expected.

Problem : JSON string

Review below example, declares a JSON string (enclosed with single or double quotes) directly.

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);
});

In Chrome, it shows following errors in console :

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

Solution : Convert JSON string to JavaScript object

To fix it, converts it to Javascript object via standard

JSON.parse()

or jQuery

$.parseJSON

.

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);
});

Note

Most web applications will return JSON formatted string directly, you need to convert it to JavaScript object before parse it with jQuery.
参考链接：http://www.mkyong.com/jquery/jquery-loop-over-json-string-each-example/