What is an HTTP Request?

With an HTTP request, a web page can make a request to, and get a response from a web server - without reloading the page. The user will stay on the same page, and he or she will not notice that scripts might request pages, or send data to a server in the background.

By using the XMLHttpRequest object, a web developer can change a page with data from the server after the page has loaded.

Google Suggest is using the XMLHttpRequest object to create a very dynamic web inte***ce: When you start typing in Google's search box, a Javascript sends the letters off to a server and the server returns a list of suggestions.

Is the XMLHttpRequest Object a W3C Standard?

The XMLHttpRequest object is not a W3C standard.

The W3C DOM Level 3 'Load and Save' specification contains some similar functionality, but these are not implemented in any browsers yet. So, at the moment, if you need to send an HTTP request from a browser, you will have to use the XMLHttpRequest object.

Creating an XMLHttpRequest Object

For Mozilla, Firefox, Safari, and Netscape:

var xmlhttp=new XMLHttpRequest()

For Internet Explorer:

var xmlhttp=new ActiveXObject('Microsoft.XMLHTTP')

Example

var xmlhttp

function loadXMLDoc(url)

{

// code for Mozilla, etc.

if (window.XMLHttpRequest)

  {

  xmlhttp=new XMLHttpRequest()

  xmlhttp.Onreadystatechange=xmlhttpChange

  xmlhttp.open('GET',url,true)

  xmlhttp.send(null)

  }

// code for IE