In Internet Explorer, you create the object using new ActiveXObject("Msxml2.XMLHTTP") or new ActiveXObject("Microsoft.XMLHTTP") depending on the version of MSXML installed. In Mozilla and Safari (and likely in future UA's that support it) you use new XMLHttpRequest() IceBrowser uses yet another method the window.createRequest() method.

var xmlhttp=false;
/*@cc_on @*/
/*@if (@_jscript_version >= 5)
// JScript gives us Conditional compilation, we can cope with old IE versions.
// and security blocked creation of the objects.
try {
  xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
  try {
   xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
  } catch (E) {
   xmlhttp = false;
  }
}
@end @*/
if (!xmlhttp && typeof XMLHttpRequest!='undefined') {
try {
  xmlhttp = new XMLHttpRequest();
} catch (e) {
  xmlhttp=false;
}
}
if (!xmlhttp && window.createRequest) {
try {
  xmlhttp = window.createRequest();
} catch (e) {
  xmlhttp=false;
}
}

2、How do I make a request?
xmlhttp.open("GET", "test.txt",true);
xmlhttp.onreadystatechange=function() {
  if (xmlhttp.readyState==4) {
   alert(xmlhttp.responseText)
  }
}
xmlhttp.send(null)

3、Making a HEAD request

xmlhttp.open("HEAD", "/faq/index.html",true);
xmlhttp.onreadystatechange=function() {
  if (xmlhttp.readyState==4) {
   alert(xmlhttp.getAllResponseHeaders())
  }
}
xmlhttp.send(null)

4、Using HEAD requests, to find the Last-Modified of another file.

xmlhttp.open("HEAD", "/faq/index.html",true);
xmlhttp.onreadystatechange=function() {
  if (xmlhttp.readyState==4) {
   alert("File was last modified on - "+
    xmlhttp.getResponseHeader("Last-Modified"))
  }
}
xmlhttp.send(null)

5、Does a url exist?
xmlhttp.open("HEAD", "/faq/index.html",true);
xmlhttp.onreadystatechange=function() {
  if (xmlhttp.readyState==4) {
   if (xmlhttp.status==200) alert("URL Exists!")
    else if (xmlhttp.status==404) alert("URL doesn't exist!")
     else alert("Status is "+xmlhttp.status)
  }
}
xmlhttp.send(null)

6、Calling a server-side Script without refreshing the page

<%
a=+(Request.QueryString('a')+'')
b=+(Request.QueryString('b')+'')
if (isNaN(a) || isNaN(b)) {a='';b='';total='' }
  else {
   total=a+b
  }
acc=Request.ServerVariables('HTTP_ACCEPT')+''
if (acc.indexOf('message/x-jl-formresult')!=-1) {
  Response.Write(total)
} else {
%>
<script src="xmlhttp.js" type="text/javascript"></script>
<script>
function calc() {
  frm=document.forms[0]
  url="add.1?a="+frm.elements['a'].value+"&b="+frm.elements['b'].value
  xmlhttp.open("GET",url,true);
  xmlhttp.onreadystatechange=function() {
   if (xmlhttp.readyState==4) {
    document.forms[0].elements['total'].value=xmlhttp.responseText
   }
  }
xmlhttp.setRequestHeader('Accept','message/x-jl-formresult')
xmlhttp.send()
return false
}
</script>
<form action="add.1" method="get" onsubmit="return calc()">
<input type=text name=a value="<%=a%>"> + <input type=text name=b value="<%=b%>">
= <input type=text name=total value="<%=total%>">
<input type=submit value="Calculate">
</form>
<%
}
%>

7、Using JSON as the transfer language

xmlhttp.open("GET","/routeplanner/airport.1?LHR",true);
xmlhttp.onreadystatechange=function() {
  if (xmlhttp.readyState==4) {
   if (xmlhttp.status!=404) {
    var local=new Function("return "+xmlhttp.responseText)();
    alert("Code - Name\n"+local[0].id+' - '+local[0].name);
   } else {
    alert("Airport not found");
   }
  }
}
xmlhttp.send(null);

8、Using XMLHTTP with GOOGLE's SOAP API

search="Word"
xmlhttp.open("POST", "http://api.google.com/search/beta2",true);
xmlhttp.onreadystatechange=function() {
  if (xmlhttp.readyState==4) {
   alert(xmlhttp.responseText)
  }
}
xmlhttp.setRequestHeader("Man", "POST http://api.google.com/search/beta2 HTTP/1.1")
xmlhttp.setRequestHeader("MessageType", "CALL")
xmlhttp.setRequestHeader("Content-Type", "text/xml")

xmlhttp.send("<?xml version='1.0' encoding='UTF-8'?>"+"\n\n"+"<SOAP-ENV:Envelope"+
      ' xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"'+
      ' xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance"'+
      ' xmlns:xsd="http://www.w3.org/1999/XMLSchema">'+
      '<SOAP-ENV:Body><ns1:doGoogleSearch'+
      ' xmlns:ns1="urn:GoogleSearch"'+
      ' SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">'+
      '<key xsi:type="xsd:string">GOOGLEKEY</key> <q'+
      ' xsi:type="xsd:string">'+search+'</q> <start'+
      ' xsi:type="xsd:int">0</start> <maxResults'+
      ' xsi:type="xsd:int">10</maxResults> <filter'+
      ' xsi:type="xsd:boolean">true</filter> <restrict'+
      ' xsi:type="xsd:string"></restrict> <safeSearch'+
      ' xsi:type="xsd:boolean">false</safeSearch> <lr'+
      ' xsi:type="xsd:string"></lr> <ie'+
      ' xsi:type="xsd:string">latin1</ie> <oe'+
      ' xsi:type="xsd:string">latin1</oe>'+
      '</ns1:doGoogleSearch>'+
    '</SOAP-ENV:Body></SOAP-ENV:Envelope>')

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