XML AJAX

AJAX is a developer's dream, because you can:

Update a web page without reloading the page
Request data from a server - after the page has loaded
Receive data from a server - after the page has loaded
Send data to a server - in the background

What is AJAX?

AJAX = Asynchronous JavaScript And XML.

AJAX is not a programming language.

AJAX just uses a combination of:

A browser built-in XMLHttpRequest object (to request data from a web server)
JavaScript and HTML DOM (to display or use the data)

The keystone of AJAX is the XMLHttpRequest object.

The XMLHttpRequest Object

All modern browsers support the XMLHttpRequest object.

The XMLHttpRequest object can be used to exchange data with a server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.

Create an XMLHttpRequest Object

All modern browsers (Chrome, Firefox, Edge (and IE7+), Safari, Opera) have a built-in XMLHttpRequest object.

Syntax for creating an XMLHttpRequest object:

variable = new XMLHttpRequest();

Example:

vvar xhttp = new XMLHttpRequest();

The "ajax_info.txt" file used in the example above, is a simple text file and looks like this:

<p>AJAX is not a programming language.</p>
<p>AJAX is a technique for accessing web servers from a web page.</p><p>AJAX stands for Asynchronous JavaScript And XML.</p>

Access Across Domains

For security reasons, modern browsers do not allow access across domains.

This means that both the web page and the XML file it tries to load, must be located on the same server.

The examples on W3Schools all open XML files located on the W3Schools domain.

If you want to use the example above on one of your own web pages, the XML files you load must be located on your own server.

REQUEST

Send a Request To a Server

To send a request to a server, we use the open() and send() methods of the XMLHttpRequest object: OPEN

Method:open(method, url, async)

Description: pecifies the type of requestmethod: the type of request: GET or POSTurl: the server (file) locationasync: true (asynchronous) or false (synchronous

Method: send()

Description: sends the request to the server (used for GET)

Method;(string)

Description: Sends the request to the server (used for POST;

GET or POST?

GET is simpler and faster than POST, and can be used in most cases.

However, always use POST requests when:

A cached file is not an option (update a file or database on the server).
Sending a large amount of data to the server (POST has no size limitations).
Sending user input (which can contain unknown characters), POST is more robust and secure than GET.

GET Requests

A simple GET request:

xhttp.open("GET", "demo_get.asp", true);

xhttp.send();

In the example above, you may get a cached result. To avoid this, add a unique ID to the URL:

xhttp.open("GET", "demo_get.asp?t=" + Math.random(), true);

xhttp.send();

If you want to send information with the GET method, add the information to the URL:

xhttp.open("GET", "demo_get2.asp?fname=Henry&lname=Ford", true);

xhttp.send();

POST Requests

A simple POST request:

xhttp.open("POST", "demo_post.asp", true);

xhttp.send();

To POST data like an HTML form, add an HTTP header with setRequestHeader(). Specify the data you want to send in the send() method:

Example

xhhttp.open("POST", "demo_post2.asp", true);

xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xhttp.send("fname=Henry&lname=Ford");

AJAX XML Example

The following example will demonstrate how a web page can fetch information from an XML file with AJAX:

Get CD info

Example Explained

When a user clicks on the "Get CD info" button above, the loadDoc() function is executed.

The loadDoc() function creates an XMLHttpRequest object, adds the function to be executed when the server response is ready, and sends the request off to the server.

When the server response is ready, an HTML table is built, nodes (elements) are extracted from the XML file, and it finally updates the element "demo" with the HTML table filled with XML data:

The XML File

The XML file used in the example above looks like this: "cd_catalog.xml".

AJAX PHP Example

The following example demonstrates how a web page can communicate with a web server while a user types characters in an input field:

EXAMPLE

Start typing a name in the input field below:

Example Explained

In the example above, when a user types a character in the input field, a function called "showHint()" is executed.

The function is triggered by the onkeyup event.

Here is the HTML code:

<html>

<head>
<script>
function showHint(str) {
    if (str.length == 0) {
        document.getElementById("txtHint").innerHTML = "";
        return;
    } else {
        var xmlhttp = new XMLHttpRequest();
        xmlhttp.onreadystatechange = function() {
            if (this.readyState == 4 && this.status == 200) {
                document.getElementById("txtHint").innerHTML = this.responseText;
            }
        };
        xmlhttp.open("GET", "gethint.php?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)">
</form>
<p>Suggestions: <span id="txtHint"></span></p>
</body>
</html>

Code explanation:

First, check if the input field is empty (str.length == 0). If it is, clear the content of the txtHint placeholder and exit the function.

However, if the input field is not empty, do the following:

Create an XMLHttpRequest object
Create the function to be executed when the server response is ready
Send the request off to a PHP file (gethint.php) on the server
Notice that q parameter is added gethint.php?q="+str
The str variable holds the content of the input field

The PHP File - "gethint.php"

The PHP file checks an array of names, and returns the corresponding name(s) to the browser:

<?php

// 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 = $_REQUEST["q"];

$hint = "";

// lookup all hints from array if $q is different from ""
if ($q !== "") {
    $q = strtolower($q);
    $len=strlen($q);
    foreach($a as $name) {
        if (stristr($q, substr($name, 0, $len))) {
            if ($hint === "") {
                $hint = $name;
          } else {
                $hint .= ", $name";
            }
        }
    }
}

// Output "no suggestion" if no hint was found or output correct values
echo $hint === "" ? "no suggestion" : $hint;
?>

AJAX is used to create more interactive applications.

AJAX ASP Example

The following example will demonstrate how a web page can communicate with a web server while a user type characters in an input field:

EXAMPLE

Start typing a name in the input field below:

Example Explained

In the example above, when a user types a character in the input field, a function called "showHint()" is executed.

The function is triggered by the onkeyup event.

Here is the HTML code:

<html>

<head>
<script>
function showHint(str) {
    if (str.length == 0) {
        document.getElementById("txtHint").innerHTML = "";
        return;
    } else {
        var xmlhttp = new XMLHttpRequest();
        xmlhttp.onreadystatechange = function() {
            if (this.readyState == 4 && this.status == 200) {
                document.getElementById("txtHint").innerHTML = this.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)">
</form>
<p>Suggestions: <span id="txtHint"></span></p>
</body>
</html>

Code explanation:

First, check if the input field is empty (str.length == 0). If it is, clear the content of the txtHint placeholder and exit the function.

However, if the input field is not empty, do the following:

Create an XMLHttpRequest object
Create the function to be executed when the server response is ready
Send the request off to an ASP file (gethint.asp) on the server
Notice that q parameter is added gethint.asp?q="+str
The str variable holds the content of the input field

The ASP File - "gethint.asp"

The ASP file checks an array of names, and returns the corresponding name(s) 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
%>

AJAX can be used for interactive communication with a database.

AJAX Database Example

The following example will demonstrate how a web page can fetch information from a database with AJAX:

Customer info will be listed here..

When a user selects a customer in the dropdown list above, a function called "showCustomer()" is executed. The function is triggered by the "onchange" event:

SHOW CUSTOMER

function showCustomer(str) {

  var xhttp;
  if (str == "") {
    document.getElementById("txtHint").innerHTML = "";
    return;
}
xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
    document.getElementById("txtHint").innerHTML = this.responseText;
    }
};
xhttp.open("GET", "getcustomer.php?q="+str, true);
xhttp.send();
}

The showCustomer() function does the following:

Check if a customer is selected
Create an XMLHttpRequest object
Create the function to be executed when the server response is ready
Send the request off to a file on the server
Notice that a parameter (q) is added to the URL (with the content of the dropdown list

AJAX Server Page

The page on the server called by the JavaScript above is an PHP file called "getcustomer.php".

The source code in "getcustomer.php" runs a query against a database, and returns the result in an HTML table:

<?php

$mysqli = new mysqli("servername", "username", "password", "dbname");
if($mysqli->connect_error) {
exit('Could not connect');
}

$sql = "SELECT customerid, companyname, contactname, address, city, postalcode, country
FROM customers WHERE customerid = ?";

$stmt = $mysqli->prepare($sql);
$stmt->bind_param("s", $_GET['q']);
$stmt->execute();
$stmt->store_result();
$stmt->bind_result($cid, $cname, $name, $adr, $city, $pcode, $country);
$stmt->fetch();
$stmt->close();

echo "<table>";
echo "<tr>";
echo "<th>CustomerID</th>";
echo "<td>" . $cid . "</td>";
echo "<th>CompanyName</th>";
echo "<td>" . $cname . "</td>";
echo "<th>ContactName</th>";
echo "<td>" . $name . "</td>";
echo "<th>Address</th>";
echo "<td>" . $adr . "</td>";
echo "<th>City</th>";
echo "<td>" . $city . "</td>";
echo "<th>PostalCode</th>";
echo "<td>" . $pcode . "</td>";
echo "<th>Country</th>";
echo "<td>" . $country . "</td>";
echo "</tr>";
echo "</table>";
?>

This chapter demonstrates some HTML applications using XML, HTTP, DOM, and JavaScript.

The XML Document Used

In this chapter we will use the XML file called "cd_catalog.xml".

Display XML Data in an HTML Table

This example loops through each <CD> element, and displays the values of the <ARTIST> and the <TITLE> elements in an HTML table:

<html>

<head>
<style>
table, th, td {
border: 1px solid black;
  border-collapse:collapse;
}
th, td {
  padding: 5px;
}
</style>
</head>
<body>

<button type="button" onclick="loadXMLDoc()">Get my CD collection</button>
<br><br>
<table id="demo"></table>

<script>
function loadXMLDoc() {
  var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
      myFunction(this);
    }
};
xmlhttp.open("GET", "cd_catalog.xml", true);
xmlhttp.send();
}
function myFunction(xml) {
  var i;
  var xmlDoc = xml.responseXML;
  var table="<tr><th>Artist</th><th>Title</th></tr>";
  var x = xmlDoc.getElementsByTagName("CD");
  for (i = 0; i <x.length; i++) {
    table += "<tr><td>" +
    x[i].getElementsByTagName("ARTIST")[0].childNodes[0].nodeValue +
    "</td><td>" +
    x[i].getElementsByTagName("TITLE")[0].childNodes[0].nodeValue +
    "</td></tr>";
}
document.getElementById("demo").innerHTML = table;
}
</script>

</body>
</htm>

Search

RaM kRisH nA

XML AJAX

What is AJAX?

The XMLHttpRequest Object

Create an XMLHttpRequest Object

Send a Request To a Server

GET Requests

POST Requests

Example

AJAX XML Example

Example Explained

The XML File

Example Explained

The PHP File - "gethint.php"

AJAX ASP Example

The ASP File - "gethint.asp"

AJAX Database Example

The XML Document Used

Display XML Data in an HTML Table