Why Ajax does not execute a callback function

Today with the Ajax POST request backstage, but always do not execute callback function, it is found that Ajax does not execute callback function for the following reasons:
The key for the JSON string returned in jquery is enclosed in quotation marks, such as {"Result": 1}.
So is the format of the data return problem, such as the datatype set to JSON, then you need to follow the format of JSON to return the data, such as set to text, there is no need to be JSON data format.

Why Ajax does not execute a callback function (GO)