ASP - AJAX and ASP

AJAX is used to create more interactive applications.

AJAX ASP Example

The example below demonstrates how a web page communicates with a web server when the user types characters in an input field:

Example

Start typing a name in the input field below:

First name:

Suggestions:


Example Explanation - HTML Page

When the user types characters in the input field above, the "showHint()" function is executed. This function is triggered by the "onkeyup" event:

<!DOCTYPE html>
<html>
<head>
<script>
function showHint(str)
{
if (str.length==0)
{
document.getElementById("txtHint").innerHTML="";
return;
}
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else
{// code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
}
}
xmlhttp.open("GET","gethint.asp?q="+str,true);
xmlhttp.send();
}
</script>
</head
<body>

<p><b>Start typing a name in the input field below:</b></p>
<form>
First name: <input type="text" onkeyup="showHint(this.value)" size="20">
</form>
<p>Suggestions: <span id="txtHint"></span></p>

</body>
</html>

Source code explanation:

If the input field is empty (str.length==0), the function clears the content of the txtHint placeholder and exits the function.

If the input field is not empty, then showHint() executes the following steps:

  • Create an XMLHttpRequest object
  • Create a function to execute when the server response is ready
  • Send a request to the file on the server
  • Note the parameter (q) added to the end of the URL (containing the content of the input field)

ASP File

The server page called via JavaScript above is an ASP file named "gethint.asp".

The source code in "gethint.asp" checks the name array, and then returns the corresponding names to the browser:

<%
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
%>

Explanation: If JavaScript sends any text (i.e., strlen($q) > 0), then the following happens:

  1. Find names that match the characters sent by JavaScript
  2. If no match is found, set the response string to "no suggestion"
  3. If one or more matching names are found, set the response string with all the names
  4. Send the response to the "txtHint" placeholder

Other extensions