[Old Pedant]

As Felgall said.

One better way (and there are others, but this works for me) is:

function createRequestObject() {
    return   ( XMLHttpRequest != null )
           ? new XMLHttpRequest( ) 
           : new ActiveXObject("Microsoft.XMLHTTP");
}

Another seemingly popular way:

function createRequestObject() 
{
    try {
        return  new XMLHttpRequest();
    } catch ( ignored ) { }
    try {
        return new ActiveXObject("Microsoft.XMLHTTP");
   } catch ( oops ) {
        return null;
   }
}