AJAX – Browser Support
The keystone of AJAX is the XMLHttpRequest object.
Different browsers use different methods to create the XMLHttpRequest object.
Internet Explorer uses an ActiveXObject, while other browsers uses the built-in JavaScript object called XMLHttpRequest.
To create this object, and deal with different browsers, we are going to use a “try and catch” statement. You can read more about the try and catch statement in our JavaScript tutorial.
Let’s update our “testAjax.htm” file with the JavaScript that creates the XMLHttpRequest object:
Example explained: First create a variable xmlHttp to hold the XMLHttpRequest object.
Then try to create the object with XMLHttp=new XMLHttpRequest(). This is for the Firefox, Opera, and Safari browsers. If that fails, try xmlHttp=new ActiveXObject(“Msxml2.XMLHTTP”) which is for Internet Explorer 6.0+, if that also fails, try xmlHttp=new ActiveXObject(“Microsoft.XMLHTTP”) which is for Internet Explorer 5.5+
If none of the three methods work, the user has a very outdated browser, and he or she will get an alert stating that the browser doesn’t support AJAX.
Note: The browser-specific code above is long and quite complex. However, this is the code you can use every time you need to create an XMLHttpRequest object, so you can just copy and paste it whenever you need it. The code above is compatible with all the popular browsers: Internet Explorer, Opera, Firefox, and Safari.
The next chapter shows how to use the XMLHttpRequest object to communicate with the server.