Ajax only gets response.readyStatus=4, but what's the reason for response.status=0?

want to cross-domain request third-party API, front end uses ajax request, backend uses superAgent as relay, but ajax can not get a response, try to output response.status=0, but is response.readyStatus=4, because the back-end response is not written correctly?

Superagent javascript node.js ajax
Apr.07,2021

readystate
status

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MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b369b6-2c023.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b369b6-2c023.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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