Why need to include dataType to JQuery ajax

Question

I have the next code:

$.ajax({
     type: "GET",
     url: url,
     data: {language: language},
     contentType: "application/json",
     success: function (result) {
        console.log(result);
        result.forEach(function(item) {
           var option = $("");
           option.text(item);
           option.val(item);
           node.append(option);
        });
        if (self.value.country) {
            $("#countrySelect").val(self.value.country);
        }
    }
});

why at first case (when I refresh page or visit it at first time) it returns json and at the next case (postback) it returns string Then I add

dataType: "json"

And now it returns only json. Why without adding it not worked correctly? 1) with dataType

2) without dataType (first load) 3) without dataType (postback)

Possible duplicate of [$.ajax - dataType](https://stackoverflow.com/questions/2722750/ajax-datatype) — Alive to die - Anant, May 02 '19 at 08:10
your route returns plain text not json so jquery doesn't know you have json, by adding the dataType you tell jquery that the string is a json object — madalinivascu, May 02 '19 at 08:14
for your route to return json you need to append the json header `Content-Type: application/json` — madalinivascu, May 02 '19 at 08:15
@madalinivascu Ok, got it, but why at first case (when I refresh page or visit it at first time it returns json) and at the next case (postback) it returns string — Enver Krynitski, May 02 '19 at 08:18
i can't tell without a closer look at your xhr request and backend route — madalinivascu, May 02 '19 at 08:20
The fix is as discussed (specify explicitly) - the cause has nothing to do with how you are calling the action, but rather what the action is returning. You've (conveniently?) left this off your images / code. There could be a subtle difference in the return value from your MVC action which means jquery doesn't recognise it as json. — freedomn-m, May 02 '19 at 08:59

score 1 · Answer 1 · answered May 02 '19 at 08:12

1

Because without specifying dataType, it takes a guess at the type. By specifying it to JSON, it will expect a JSON data response. You also can't specify multiple data types - if you need different data types returned, you have to leave it set to the default value.

answered May 02 '19 at 08:12

Jack Bashford

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but why at first case (when I refresh page or visit it at first time it returns json) and at the next case (postback) it returns string – Enver Krynitski May 02 '19 at 08:18

Why need to include dataType to JQuery ajax

1 Answers1