//Create a boolean variable to check for a valid Internet Explorer instance.
var xmlhttp = false;
//Check if we are using IE.
try {
//If the Javascript version is greater than 5.
xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
alert ("You are using Microsoft Internet Explorer.");
} catch (e) {

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CHAPTER 2  AJAX BASICS18
//If not, then use the older active x object.
try {
//If we are using Internet Explorer.
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
alert ("You are using Microsoft Internet Explorer");
} catch (E) {
//Else we must be using a non-IE browser.
xmlhttp = false;
}
//If we are using a non-IE browser, create a javascript instance of the object.
if (!xmlhttp && typeof XMLHttpRequest != 'undefined') {
xmlhttp = new XMLHttpRequest();
alert ("You are not using Microsoft Internet Explorer");
}