Javascript Ajax obtains remote url return judgment

Copy codeThe Code is as follows:
<Script language = "JavaScript">
<! --
Function ajaxByJyking (){
Var xmlhttp_request = "";
Try {
If (window. ActiveXObject ){
For (var I = 5; I --){
Try {
If (I = 2 ){
Xmlhttp_request = new ActiveXObject ("Microsoft. XMLHTTP ");}
Else {
Xmlhttp_request = new ActiveXObject ("Msxml2.XMLHTTP." + I + ". 0 ");
Xmlhttp_request.setRequestHeader ("Content-Type", "text/xml ");
Xmlhttp_request.setRequestHeader ("Charset", "gb2312 ");}
Break ;}
Catch (e ){
Xmlhttp_request = false ;}}}
Else if (window. XMLHttpRequest)
{Xmlhttp_request = new XMLHttpRequest ();
If (xmlhttp_request.overrideMimeType)
{Xmlhttp_request.override.MimeType ('text/xml ');}}}
Catch (e) {xmlhttp_request = false ;}
Xmlhttp_request.open ('get', 'HTTP: // www.jb51.net', true );
Xmlhttp_request.send (null );
Xmlhttp_request.onreadystatechange = function (){
If (xmlhttp_request.readyState = 4 ){
// Receives the complete Server Response
Document. write ("yes ")
} Else {
Alert (1)
}
}
}
AjaxByJyking ();
// -->
</SCRIPT>