Use of jQuery ajaxjsonp for cross-origin requests

An ajaxjsonp written in the project the day before yesterday has a problem: the request result can be obtained successfully, however, if the success method is not executed, the error method is directly executed, indicating an error -- ajax jsonp has never been used before. Its understanding is similar to that of common ajax requests, but it is not well understood; after debugging (checking the backend code and js attribute settings), I am surprised and puzzled. Therefore, I decided to carefully study the use of ajax jsonp and share my learning experience on the success of the test!
First, paste the code that can be successfully executed:
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