The execution order of ajax, whether to execute onreadystatechange first or open first.


< html >
< head >
< meta charset= "utf-8" >
< script >
function showHint (str)
{
var xmlhttp;
if (str.length==0)
{

document.getElementById("txtHint").innerHTML="";
return;

}
if (window.XMLHttpRequest)
{

// IE7+, Firefox, Chrome, Opera, Safari 
xmlhttp=new XMLHttpRequest();

}
else
{

// IE6, IE5 
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");

}
xmlhttp.onreadystatechange=function ()
{

if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
  document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
}

}
xmlhttp.open ("GET", "/ try/ajax/gethint.php?q=" + str,true);
xmlhttp.send ();
}
< / script >
< / head >
< body >

in the input box, try entering the letters a:


< form action= "" >
enter the name: < input type= "text" id= "txt1" onkeyup= "showHint (this.value)" / >
< / form >

prompt: < span id= "txtHint" >

< / body >
< / html >

Mar.28,2021

execute the open function first.

onreadystatechange is a status monitoring function. The ajax request has five states of 0-4. The default is 0 (the request is not initialized when the), open () establishes a connection. After the open opens the connection, the status of the ajax becomes 1. This will execute the onreadystatechange, once and onreadystatechange will be run once when the connection status changes to 2, 3 and 4.

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