AJAX - onreadystatechange ???

onreadystatechange ???

??? ??? ???? ? ?? ?? ?? ??? ???? ???.

readyState? ??? ??? onreadystatechange ???? ??????.

readyState ??? XMLHttpRequest? ?? ??? ?????.

??? XMLHttpRequest ??? ? ?? ??? ?????:

????????????????????????????????????????????????????????????????????????????????????????????????? ??? ?????. readyState

XMLHttpRequest? ??? ?????. 0?? 4? ?????. 0: ??? ????? ???? ?????

1: ?? ??? ???????

2: ??? ???????

3: ?? ?? ?

4: ??? ?????? ??? ???????

?? 200: "OK" 404: ???? ?? ? ??

onreadystatechange ?????? ?? ??? ??? ??? ??? ? ??? ??? ?????.

readyState? 4?? ??? 200?? ??? ?????? ?????.

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

??: onreadystatechange ???? ? ReadyState ??? ?? 5?(0 - 4) ??????.

?? ?? ????

?? ??? ?? ??? ????? ???? ?????.

? ???? ?? AJAX ??? ?? ?? XMLHttpRequest ??? ???? ?? ?? ??? ???? ? AJAX ??? ?? ? ??? ???? ???.

?? ???? onreadystatechange ???? ??? ? ??? URL? ??? ????? ???(???? ?? ? ??):

function myFunction()
{
loadXMLDoc("ajax_info.txt",function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
    }
  });
}

???? ??

??? ??

<!DOCTYPE html> <html> <head> <script> var xmlhttp; function loadXMLDoc(url,cfunc) { if (window.XMLHttpRequest) {// IE7+, Firefox, Chrome, Opera, Safari 代碼 xmlhttp=new XMLHttpRequest(); } else {// IE6, IE5 代碼 xmlhttp=new ActiveXObject("Microsoft.XMLHTTP"); } xmlhttp.onreadystatechange=cfunc; xmlhttp.open("GET",url,true); xmlhttp.send(); } function myFunction() { loadXMLDoc("/asset/demo.ajax.php?dm=txt",function() { if (xmlhttp.readyState==4 && xmlhttp.status==200) { document.getElementById("myDiv").innerHTML=xmlhttp.responseText; } }); } </script> </head> <body> <div id="myDiv"><h2>修改文本內(nèi)容</h2></div> <button type="button" onclick="myFunction()">點(diǎn)擊</button> </body> </html>

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