Send JSON data with jQuery

Question

Why code below sent data as City=Moscow&Age=25 instead of JSON format?

var arr = {City:'Moscow', Age:25}; $.ajax(    {         url: "Ajax.ashx",         type: "POST",         data: arr,         dataType: 'json',         async: false,         success: function(msg) {             alert(msg);         }     } ); 

Answer 1

Because you haven't specified neither request content type, nor correct JSON request. Here's the correct way to send a JSON request:

var arr = { City: 'Moscow', Age: 25 }; $.ajax({     url: 'Ajax.ashx',     type: 'POST',     data: JSON.stringify(arr),     contentType: 'application/json; charset=utf-8',     dataType: 'json',     async: false,     success: function(msg) {         alert(msg);     } }); 

Things to notice:

• Usage of the JSON.stringify method to convert a javascript object into a JSON string which is native and built-into modern browsers. If you want to support older browsers you might need to include json2.js
• Specifying the request content type using the contentType property in order to indicate to the server the intent of sending a JSON request
• The dataType: 'json' property is used for the response type you expect from the server. jQuery is intelligent enough to guess it from the server Content-Type response header. So if you have a web server which respects more or less the HTTP protocol and responds with Content-Type: application/json to your request jQuery will automatically parse the response into a javascript object into the success callback so that you don't need to specify the dataType property.

Things to be careful about:

• What you call arr is not an array. It is a javascript object with properties (City and Age). Arrays are denoted with [] in javascript. For example [{ City: 'Moscow', Age: 25 }, { City: 'Paris', Age: 30 }] is an array of 2 objects.

Answer 2

Because by default jQuery serializes objects passed as the data parameter to $.ajax. It uses $.param to convert the data to a query string.

From the jQuery docs for $.ajax:

[the data argument] is converted to a query string, if not already a string

If you want to send JSON, you'll have to encode it yourself:

data: JSON.stringify(arr); 

Note that JSON.stringify is only present in modern browsers. For legacy support, look into json2.js