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HarmonyOS
<!DOCTYPE html>
<html>
<head>
<title>Ajax</title>
</head>
<body>
<div id = "new"></div>
<script type="text/javascript" src = "scripts/addLoadEvent.js"></script>
<script type="text/javascript" src = "scripts/getHTTPObject.js"></script>
<script type="text/javascript" src = "scripts/getNewContent.js"></script>
</body>
</html>
function addLoadEvent(func){
if( typeof window.onload != "function"){
window.onload = func;
}else{
window.onload = function(){
oldload();
func();
}
}
}
function getHTTPObject(){
if(typeof XMLHttpRequest == "undefined"){
XMLHttpRequest = function(){
try { return new ActiveXObject("Msxml2.XMLHTTP.6.0");}
catch(e){}
try { return new ActiveXObject("Msxml2.XMLHTTP.3.0");}
catch(e){}
try { return new ActiveXObject("Msxml2.XMLHTTP");}
catch(e){}
return false;
}
}
return new XMLHttpRequest();
}
function getNewContent(){
var request = getHTTPObject();
if(request) {
request.open("GET", "example.txt", true);
request.onreadystatechange = function(){
if(request.readyState == 4) {
var para = document.createElement("p");
var txt = document.createTextNode(request.responseText);
para.appendChild(txt);
document.getElementById('new').appendChild(para);
}
};
request.send(null);
}else{
alert("Sorry , your browser doesn\'t support XMLHttpRequest");
}
}
addLoadEvent(getNewContent);
这是书上关于ajax的一个例子，用ctrl+o在chrome浏览器成功运行，关于最后一个getNewContent函数，我想问request.send（null）为什么写在后面？？？
触发onreadyState的过程是异步的,所以同步的执行request.send()，放在前后关系不大