The order problem of xmlHttp.onreadystatechange

I have seen many ways to write 

    xmlHttp.open("post", "test.php",true); 
    xmlHttp.send(formData); 
    xmlHttp.onreadystatechange =  function(){  }

xmlHttp.onreadystatechange first 


    xmlHttp.onreadystatechange =  function(){  }
    xmlHttp.open("post", "test.php",true); 
    xmlHttp.send(formData);

there is another such

xmlhttp.open ("POST", "Demo", true);
xmlhttp.onreadystatechange=myCallBack;
xmlhttp.setRequestHeader ("Content-Type", "application/x-www-form-urlencoded;charset=UTF-8");
xmlhttp.send ("FirstName=Nat&LastName=Dunn");

excuse me, 

xmlHttp.open 
xmlHttp.send 
xmlHttp.onreadystatechange =
Javascript
Dec.12,2021

1. Open the request. 2 send the request. 3 request complete.

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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-64f5-1b3c60b-2c320.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3c60b-2c320.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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