Under what circumstances will Ajax go success and error

Simply put, the AJAX request sends a request through the XMLHttpRequest object, which has four states (ReadyState):

0-Uninitialized, 1-initializing, 2-sending data, 3-sending data, 4-complete.

When Xmlhttprequest.readystate is 4 o'clock, it indicates that the AJAX request has been completed to get the response result.

The success and error methods of Ajax are triggered according to the response status code. When Xmlhttprequest.status is 200, the response is successful and success () is triggered. Other Status Codes trigger error ().

In addition to the response status code, AJAX will take the error method in the following cases:

1. The return data type does not match the datatype

2. Network outages

3. Background response interruption

Under what circumstances will Ajax go success and error