Why did reader.onprogress monitor the data only once?

problem description

the data is displayed only once in console every time the picture is loaded, so it is suspected that onprogress is not listening all the time.

the environmental background of the problems and what methods you have tried

related codes

/ / Please paste the code text below (do not replace the code with pictures)

reader.onprogress = function(e) {
            
            if (e.lengthComputable) {
              let percent = Math.round(e.loaded / e.total * 100);
                 console.log(e.loaded);
              
            }
          };

what result do you expect? What is the error message actually seen?

should display a series of e.loaded like a waterfall

Mar.31,2021
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-64f5-1b3eb19-4dad0.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3eb19-4dad0.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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