Get the width of the Element-ui table header

tries to use ref, which returns a real example of a component, and then I don"t know what to do with how to get the width of header.

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-64f5-1e96055-15a1.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e96055-15a1.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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