As you can see, the HTML page above contains a simple HTML form with an input field called "txt1".
The form works like this:
An event is triggered when the user presses, and releases a key in the input field
When the event is triggered, a function called showHint() is executed.
Below the form is a called "txtHint". This is used as a placeholder for the return data of the showHint() function.
JavaScript :
The JavaScript code is stored in "clienthint.js" and linked to the HTML document:
CODE/PROGRAM/EXAMPLE
var xmlHttp
function showHint(str)
{
if (str.length==0)
{
document.getElementById("txtHint").innerHTML=""
return
}
xmlHttp=GetXmlHttpObject()
if (xmlHttp==null)
{
alert ("Browser does not support HTTP Request")
return
}
var url="gethint.php"
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 || xmlHttp.readyState=="complete")
{
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;
}
Example Explained :
The showHint() Function
This 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
Calls on the GetXmlHttpObject function to create 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.
stateChanged() Function :
This function executes every time the state of the XMLHTTP object changes. When the state changes to 4 (or to "complete"), the content of the txtHint placeholder is filled with the response text.
GetXmlHttpObject() Function :
AJAX applications can only run in web browsers with complete XML support.
The code above called a function called GetXmlHttpObject().
The purpose of the function is to solve the problem of creating different XMLHTTP objects for different browsers.
This is explained in the previous chapter.
PHP Page :
The server page called by the JavaScript code is a simple PHP file called "gethint.php".
The code in the "gethint.php" checks an array of names and returns the corresponding names to
the client:
CODE/PROGRAM/EXAMPLE
<?php
// 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; $i<count($a); $i++)
{
if (strtolower($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 $response;
?>
If there is any text sent from the JavaScript (strlen($q) > 0) the following happens:
Find a name matching the characters sent from the JavaScript
If more than one name is found, include all names in the response string
If no matching names were found, set response to "no suggestion"
If one or more matching names were found, set response to these names
