AJAX - in a simple way

AJAX - More About the XMLHttpRequest Object

Before sending data to the server, we have to explain three important properties of the XMLHttpRequest object.

The onreadystatechange Property

After a request to the server, we need a function that can receive the data that is returned by the server.

The onreadystatechange property stores the function that will process the response from a server. The following code defines an empty function and sets the onreadystatechange property at the same time:

xmlHttp.onreadystatechange=function()

{

// We are going to write some code here

}

The readyState Property

The readyState property holds the status of the server's response. Each time the readyState changes, the onreadystatechange function will be executed.

Here are the possible values for the readyState property:

State

Description

0

The request is not initialized

1

The request has been set up

2

The request has been sent

3

The request is in process

4

The request is complete

We are going to add an If statement to the onreadystatechange function to test if our response is complete (this means that we can get our data):

xmlHttp.onreadystatechange=function()

{

if(xmlHttp.readyState==4)

{

// Get the data from the server's response

}

}

The responseText Property

The data sent back from the server can be retrieved with the responseText property.

In our code, we will set the value of our "time" input field equal to responseText:

xmlHttp.onreadystatechange=function()

{

if(xmlHttp.readyState==4)

{

document.myForm.time.value=xmlHttp.responseText;

}

}

AJAX - Sending a Request to the Server

To send off a request to the server, we use the open() method and the send() method.

The open() method takes three arguments. The first argument defines which method to use when sending the request (GET or POST). The second argument specifies the URL of the server-side script. The third argument specifies that the request should be handled asynchronously. The send() method sends the request off to the server. If we assume that the HTML and ASP file are in the same directory, the code would be:

xmlHttp.open("GET","time.asp",true);

xmlHttp.send(null);

Now we must decide when the AJAX function should be executed. We will let the function run "behind the scenes" when the user types something in the username text field:

Name:

onkeyup="ajaxFunction();" name="username" />

Time:

Our updated AJAX-ready "testAjax.htm" file now looks like this:


Name:

onkeyup="ajaxFunction();" name="username" />

Time:

AJAX - The Server-Side ASP Script

Now we are going to create the script that displays the current server time.

The responseText property (explained in the previous chapter) will store the data returned from the server. Here we want to send back the current time. The code in "time.asp" looks like this:

<%
response.expires=-1
response.write(time)
%>

Note: The Expires property sets how long (in minutes) a page will be cached on a browser before it expires. If a user returns to the same page before it expires, the cached version is displayed. Response.Expires=-1 indicates that the page will never be cached.

Run Your AJAX Application

Try the AJAX application by typing some text into the Name text box below, then click inside the Time text box:

Name: Time:

We have seen that AJAX can be used to create more interactive applications.

AJAX Suggest Example

In the AJAX example below we will demonstrate how a web page can communicate with a web server online as a user enters data into a standard HTML form.

Type a Name in the Box Below

First Name:

Suggestions:

Example Explained - The HTML Form

The form above has the following HTML code:

 
First Name:
onkeyup="showHint(this.value)">
Suggestions:

As you can see it is just a simple HTML form with an input field called "txt1".

An event attribute for the input field defines a function to be triggered by the onkeyup event.

The paragraph below the form contains a span called "txtHint". The span is used as a placeholder for data retrieved from the web server.

When the user inputs data, a function called "showHint()" is executed. The execution of the function is triggered by the "onkeyup" event. In other words: Each time the user moves his finger away from a keyboard key inside the input field, the function showHint is called.

Example Explained - The showHint() Function

The showHint() function is a very simple JavaScript function placed in the section of the HTML page.

The function contains the following code:

function showHint(str)
{
if (str.length==0)
  { 
  document.getElementById("txtHint").innerHTML="";
  return;
  }
xmlHttp=GetXmlHttpObject();
if (xmlHttp==null)
  {
  alert ("Your browser does not support AJAX!");
  return;
  } 
var url="gethint.asp";
url=url+"?q="+str;
url=url+"&sid="+Math.random();
xmlHttp.onreadystatechange=stateChanged;
xmlHttp.open("GET",url,true);
xmlHttp.send(null);
}

The function executes every time a character is entered in the input field.

If there is some input in the text field (str.length > 0) the function executes the following:

  • Defines the url (filename) to send to the server
  • Adds a parameter (q) to the url with the content of the input field
  • Adds a random number to prevent the server from using a cached file
  • Creates an XMLHTTP object, and tells the object to execute a function called stateChanged when a change is triggered
  • Opens the XMLHTTP object with the given url.
  • Sends an HTTP request to the server

If the input field is empty, the function simply clears the content of the txtHint placeholder.

Example Explained - The GetXmlHttpObject() Function

The example above calls a function called GetXmlHttpObject().

The purpose of the function is to solve the problem of creating different XMLHTTP objects for different browsers.

The function is listed below:

function GetXmlHttpObject()
{
var xmlHttp=null;
try
  {
  // Firefox, Opera 8.0+, Safari
  xmlHttp=new XMLHttpRequest();
  }
catch (e)
  {
  // Internet Explorer
  try
    {
    xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
    }
  catch (e)
    {
    xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
  }
return xmlHttp;
}

Example Explained - The stateChanged() Function

The stateChanged() function contains the following code:

function stateChanged() 
{ 
if (xmlHttp.readyState==4)
{ 
document.getElementById("txtHint").innerHTML=xmlHttp.responseText;
}
}

The stateChanged() function executes every time the state of the XMLHTTP object changes.

When the state changes to 4 ("complete"), the content of the txtHint placeholder is filled with the response text.

AJAX Source Code to Suggest Example

The source code below belongs to the AJAX example on the previous page.

You can copy and paste it, and try it yourself.

The AJAX HTML Page

This is the HTML page. It contains a simple HTML form and a link to a JavaScript.

 
 
First Name:
onkeyup="showHint(this.value)">
Suggestions:

The JavaScript code is listed below.

The AJAX JavaScript

This is the JavaScript code, stored in the file "clienthint.js":

var xmlHttp
 
function showHint(str)
{
if (str.length==0)
  { 
  document.getElementById("txtHint").innerHTML="";
  return;
  }
xmlHttp=GetXmlHttpObject();
if (xmlHttp==null)
  {
  alert ("Your browser does not support AJAX!");
  return;
  } 
var url="gethint.asp";
url=url+"?q="+str;
url=url+"&sid="+Math.random();
xmlHttp.onreadystatechange=stateChanged;
xmlHttp.open("GET",url,true);
xmlHttp.send(null);
} 
 
function stateChanged() 
{ 
if (xmlHttp.readyState==4)
{ 
document.getElementById("txtHint").innerHTML=xmlHttp.responseText;
}
}
 
function GetXmlHttpObject()
{
var xmlHttp=null;
try
  {
  // Firefox, Opera 8.0+, Safari
  xmlHttp=new XMLHttpRequest();
  }
catch (e)
  {
  // Internet Explorer
  try
    {
    xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
    }
  catch (e)
    {
    xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
  }
return xmlHttp;
}

The AJAX Server Page - ASP and PHP

There is no such thing as an AJAX server. AJAX pages can be served by any internet server.

The server page called by the JavaScript in the example from the previous chapter is a simple ASP file called "gethint.asp".

Below we have listed two examples of the server page code, one written in ASP and one in PHP.

AJAX ASP Example

The code in the "gethint.asp" page is written in VBScript for an Internet Information Server (IIS). It just checks an array of names and returns the corresponding names to the client:

<%
response.expires=-1
dim a(30)
'Fill up array with names
a(1)="Anna"
a(2)="Brittany"
a(3)="Cinderella"
a(4)="Diana"
a(5)="Eva"
a(6)="Fiona"
a(7)="Gunda"
a(8)="Hege"
a(9)="Inga"
a(10)="Johanna"
a(11)="Kitty"
a(12)="Linda"
a(13)="Nina"
a(14)="Ophelia"
a(15)="Petunia"
a(16)="Amanda"
a(17)="Raquel"
a(18)="Cindy"
a(19)="Doris"
a(20)="Eve"
a(21)="Evita"
a(22)="Sunniva"
a(23)="Tove"
a(24)="Unni"
a(25)="Violet"
a(26)="Liza"
a(27)="Elizabeth"
a(28)="Ellen"
a(29)="Wenche"
a(30)="Vicky"
'get the q parameter from URL
q=ucase(request.querystring("q"))
'lookup all hints from array if length of q>0
if len(q)>0 then
  hint=""
  for i=1 to 30
    if q=ucase(mid(a(i),1,len(q))) then
      if hint="" then
        hint=a(i)
      else
        hint=hint & " , " & a(i)
      end if
    end if
  next
end if
'Output "no suggestion" if no hint were found
'or output the correct values
if hint="" then 
  response.write("no suggestion")
else
  response.write(hint)
end if
%>

AJAX PHP Example

The code above rewritten in PHP.

Note: To run the entire example in PHP, remember to change the value of the url variable in "clienthint.js" from "gethint.asp" to "gethint.php".

PHP Example

header("Cache-Control: no-cache, must-revalidate");
 // Date in the past
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
 
// Fill up array with names
$a[]="Anna";
$a[]="Brittany";
$a[]="Cinderella";
$a[]="Diana";
$a[]="Eva";
$a[]="Fiona";
$a[]="Gunda";
$a[]="Hege";
$a[]="Inga";
$a[]="Johanna";
$a[]="Kitty";
$a[]="Linda";
$a[]="Nina";
$a[]="Ophelia";
$a[]="Petunia";
$a[]="Amanda";
$a[]="Raquel";
$a[]="Cindy";
$a[]="Doris";
$a[]="Eve";
$a[]="Evita";
$a[]="Sunniva";
$a[]="Tove";
$a[]="Unni";
$a[]="Violet";
$a[]="Liza";
$a[]="Elizabeth";
$a[]="Ellen";
$a[]="Wenche";
$a[]="Vicky";
//get the q parameter from URL
$q=$_GET["q"];
//lookup all hints from array if length of q>0
if (strlen($q) > 0)
{
  $hint="";
  for($i=0; $i
  {
  if (strtolower($q)==strtolower(substr($a[$i],0,strlen($q))))
    {
    if ($hint=="")
      {
      $hint=$a[$i];
      }
    else
      {
      $hint=$hint." , ".$a[$i];
      }
    }
  }
}
 
// Set output to "no suggestion" if no hint were found
// or to the correct values
if ($hint == "")
{
$response="no suggestion";
}
else
{
$response=$hint;
}
 
//output the response
echo $response;
?>

AJAX can be used for interactive communication with a database.

AJAX Database Example

In the AJAX example below we will demonstrate how a web page can fetch information from a database using AJAX technology.

Select a Name in the Box Below

Select a Customer:

Customer info will be listed here.

AJAX Example Explained

The example above contains a simple HTML form and a link to a JavaScript:

 
Select a Customer:
Customer info will be listed here.

As you can see it is just a simple HTML form with a drop down box called "customers".

The paragraph below the form contains a div called "txtHint". The div is used as a placeholder for info retrieved from the web server.

When the user selects data, a function called "showCustomer()" is executed. The execution of the function is triggered by the "onchange" event. In other words: Each time the user change the value in the drop down box, the function showCustomer is called.

The JavaScript code is listed below.

The AJAX JavaScript

This is the JavaScript code stored in the file "selectcustomer.js":

var xmlHttp
 
function showCustomer(str)
{ 
xmlHttp=GetXmlHttpObject();
if (xmlHttp==null)
  {
  alert ("Your browser does not support AJAX!");
  return;
  } 
var url="getcustomer.asp";
url=url+"?q="+str;
url=url+"&sid="+Math.random();
xmlHttp.onreadystatechange=stateChanged;
xmlHttp.open("GET",url,true);
xmlHttp.send(null);
}
 
function stateChanged() 
{ 
if (xmlHttp.readyState==4)
{ 
document.getElementById("txtHint").innerHTML=xmlHttp.responseText;
}
}
 
function GetXmlHttpObject()
{
var xmlHttp=null;
try
  {
  // Firefox, Opera 8.0+, Safari
  xmlHttp=new XMLHttpRequest();
  }
catch (e)
  {
  // Internet Explorer
  try
    {
    xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
    }
  catch (e)
    {
    xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
  }
return xmlHttp;
}

The AJAX Server Page

The server page called by the JavaScript, is a simple ASP file called "getcustomer.asp".

The page is written in VBScript for an Internet Information Server (IIS). It could easily be rewritten in PHP, or some other server language. Look at a corresponding example in PHP.

The code runs an SQL against a database and returns the result as an HTML table:

<%
response.expires=-1
sql="SELECT * FROM CUSTOMERS WHERE CUSTOMERID="
sql=sql & "'" & request.querystring("q") & "'"
 
set conn=Server.CreateObject("ADODB.Connection")
conn.Provider="Microsoft.Jet.OLEDB.4.0"
conn.Open(Server.Mappath("/db/northwind.mdb"))
set rs = Server.CreateObject("ADODB.recordset")
rs.Open sql, conn
 
response.write("")
do until rs.EOF
  for each x in rs.Fields
    response.write("
")
    response.write("
")
  next
  rs.MoveNext
loop
 
response.write("
" & x.name & "" & x.value & "
")
%>

AJAX can be used for interactive communication with an XML file.

AJAX XML Example

In the AJAX example below we will demonstrate how a web page can fetch information from an XML file using AJAX technology.

Select a CD in the Box Below

Select a CD:

CD info will be listed here.

AJAX Example Explained

The example above contains a simple HTML form and a link to a JavaScript:

 
Select a CD:
CD info will be listed here.

As you can see it is just a simple HTML form with a simple drop down box called "cds".

The paragraph below the form contains a div called "txtHint". The div is used as a placeholder for info retrieved from the web server.

When the user selects data, a function called "showCD" is executed. The execution of the function is triggered by the "onchange" event. In other words: Each time the user change the value in the drop down box, the function showCD is called.

The JavaScript code is listed below.

The AJAX JavaScript

This is the JavaScript code stored in the file "selectcd.js":

var xmlHttp
function showCD(str)
{ 
xmlHttp=GetXmlHttpObject();
if (xmlHttp==null)
  {
  alert ("Your browser does not support AJAX!");
  return;
  } 
var url="getcd.asp";
url=url+"?q="+str;
url=url+"&sid="+Math.random();
xmlHttp.onreadystatechange=stateChanged;
xmlHttp.open("GET",url,true);
xmlHttp.send(null);
}
function stateChanged() 
{ 
if (xmlHttp.readyState==4)
{ 
document.getElementById("txtHint").innerHTML=xmlHttp.responseText;
}
}
function GetXmlHttpObject()
{
var xmlHttp=null;
try
  {
  // Firefox, Opera 8.0+, Safari
  xmlHttp=new XMLHttpRequest();
  }
catch (e)
  {
  // Internet Explorer
  try
    {
    xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
    }
  catch (e)
    {
    xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
  }
return xmlHttp;
}

The XML File

The XML file is "cd_catalog.xml". This document contains a CD collection.

The AJAX Server Page

The server page called by the JavaScript, is a simple ASP file called "getcd.asp".

The page is written in VBScript for an Internet Information Server (IIS). It could easily be rewritten in PHP, or some other server language. Look at a corresponding example in PHP.

The code runs a query against an XML file and returns the result as HTML:

<%
response.expires=-1
q=request.querystring("q")
 
set xmlDoc=Server.CreateObject("Microsoft.XMLDOM")
xmlDoc.async="false"
xmlDoc.load(Server.MapPath("cd_catalog.xml"))
 
set nodes=xmlDoc.selectNodes("CATALOG/CD[ARTIST='" & q & "']")
 
for each x in nodes
  for each y in x.childnodes
    response.write("" & y.nodename & ": ")
    response.write(y.text)
    response.write("

")
  next
next
%>

While responseText returns the HTTP response as a string, responseXML returns the response as XML.

The ResponseXML property returns an XML document object, which can be examined and parsed using W3C DOM node tree methods and properties.

AJAX ResponseXML Example

In the following AJAX example we will demonstrate how a web page can fetch information from a database using AJAX technology. The selected data from the database will this time be converted to an XML document, and then we will use the DOM to extract the values to be displayed.

Select a Name in the Box Below

Select a Customer:






AJAX Example Explained

The example above contains an HTML form, several elements to hold the returned data, and a link to a JavaScript:

 
Select a Customer:

The example above contains an HTML form with a drop down box called "customers".

When the user selects a customer in the dropdown box, a function called "showCustomer()" is executed. The execution of the function is triggered by the "onchange" event. In other words: Each time the user change the value in the drop down box, the function showCustomer() is called.

The JavaScript code is listed below.

The AJAX JavaScript

This is the JavaScript code stored in the file "selectcustomer_xml.js":

var xmlHttp
function showCustomer(str)
{ 
xmlHttp=GetXmlHttpObject();
if (xmlHttp==null)
  {
  alert ("Your browser does not support AJAX!");
  return;
  }
var url="getcustomer_xml.asp";
url=url+"?q="+str;
url=url+"&sid="+Math.random();
xmlHttp.onreadystatechange=stateChanged;
xmlHttp.open("GET",url,true);
xmlHttp.send(null);
}
function stateChanged() 
{ 
if (xmlHttp.readyState==4)
{
var xmlDoc=xmlHttp.responseXML.documentElement;
document.getElementById("companyname").innerHTML=
xmlDoc.getElementsByTagName("compname")[0].childNodes[0].nodeValue;
document.getElementById("contactname").innerHTML=
xmlDoc.getElementsByTagName("contname")[0].childNodes[0].nodeValue;
document.getElementById("address").innerHTML=
xmlDoc.getElementsByTagName("address")[0].childNodes[0].nodeValue;
document.getElementById("city").innerHTML=
xmlDoc.getElementsByTagName("city")[0].childNodes[0].nodeValue;
document.getElementById("country").innerHTML=
xmlDoc.getElementsByTagName("country")[0].childNodes[0].nodeValue;
}
}
 
function GetXmlHttpObject()
{
var xmlHttp=null;
try
  {
  // Firefox, Opera 8.0+, Safari
  xmlHttp=new XMLHttpRequest();
  }
catch (e)
  {
  // Internet Explorer
  try
    {
    xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
    }
  catch (e)
    {
    xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
  }
return xmlHttp;
}

The showCustomer() and GetXmlHttpObject() functions above are the same as in previous chapters. The stateChanged() function is also used earlier in this tutorial, however; this time we return the result as an XML document (with responseXML) and uses the DOM to extract the values we want to be displayed.

The AJAX Server Page

The server page called by the JavaScript, is a simple ASP file called "getcustomer_xml.asp".

The page is written in VBScript for an Internet Information Server (IIS). It could easily be rewritten in PHP, or some other server language. Look at a corresponding example in PHP.

The code runs an SQL query against a database and returns the result as an XML document:

<%
response.expires=-1
response.contenttype="text/xml"
sql="SELECT * FROM CUSTOMERS "
sql=sql & " WHERE CUSTOMERID='" & request.querystring("q") & "'"
 
on error resume next
set conn=Server.CreateObject("ADODB.Connection")
conn.Provider="Microsoft.Jet.OLEDB.4.0"
conn.Open(Server.Mappath("/db/northwind.mdb"))
set rs=Server.CreateObject("ADODB.recordset")
rs.Open sql, conn
if err <> 0 then
response.write(err.description)
set rs=nothing
set conn=nothing
else
response.write("")
response.write("")
response.write("" &rs.fields("companyname")& "")
response.write("" &rs.fields("contactname")& "")
response.write("
" &rs.fields("address")& "
")
response.write("" &rs.fields("city")& "")
response.write("" &rs.fields("country")& "")
response.write("")
end if
on error goto 0
%>

Notice the second line in the ASP code above: response.contenttype="text/xml". The ContentType property sets the HTTP content type for the response object. The default value for this property is "text/html". This time we want the content type to be XML.

Then we select data from the database, and builds an XML document with the data.

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