Ajax

AJAX is about updating parts of a web page, without reloading the whole page.

What is AJAX?

AJAX = Asynchronous JavaScript and XML.

AJAX is a technique for creating fast and dynamic web pages.

AJAX allows web pages to be updated asynchronously by exchanging small amounts of data with the server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.

Classic web pages, (which do not use AJAX) must reload the entire page if the content should change.

Examples of applications using AJAX: Google Maps, Gmail, Youtube, and Facebook tabs.

AJAX is based on internet standards, and uses a combination of:

XMLHttpRequest object (to exchange data asynchronously with a server)
JavaScript/DOM (to display/interact with the information)
CSS (to style the data)
XML (often used as the format for transferring data)

AJAX applications are browser- and platform-independent!

AJAX and PHP

<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 action="">
  <label for="fname">First name:</label>
  <input type="text" id="fname" name="fname" onkeyup="showHint(this.value)">
</form>
<p>Suggestions: <span id="txtHint"></span></p>
</body>
</html>

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 and MySQL

AJAX can be used for interactive communication with a database.

The database table we use in the example above looks like this:

id	FirstName	LastName	Age	Hometown	Job
1	Peter	Griffin	41	Quahog	Brewery
2	Lois	Griffin	40	Newport	Piano Teacher
3	Joseph	Swanson	39	Quahog	Police Officer
4	Glenn	Quagmire	41	Quahog	Pilot

<html>
<head>
<script>
function showUser(str) {
  if (str == "") {
    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","getuser.php?q="+str,true);
    xmlhttp.send();
  }
}
</script>
</head>
<body>

<form>
<select name="users" onchange="showUser(this.value)">
  <option value="">Select a person:</option>
  <option value="1">Peter Griffin</option>
  <option value="2">Lois Griffin</option>
  <option value="3">Joseph Swanson</option>
  <option value="4">Glenn Quagmire</option>
  </select>
</form>
<br>
<div id="txtHint"><b>Person info will be listed here...</b></div>

</body>
</html>

The page on the server called by the JavaScript above is a PHP file called "getuser.php".

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

<!DOCTYPE html>
<html>
<head>
<style>
table {
  width: 100%;
  border-collapse: collapse;
}

table, td, th {
  border: 1px solid black;
  padding: 5px;
}

th {text-align: left;}
</style>
</head>
<body>

<?php
$q = intval($_GET['q']);

$con = mysqli_connect('localhost','peter','abc123');
if (!$con) {
  die('Could not connect: ' . mysqli_error($con));
}

mysqli_select_db($con,"ajax_demo");
$sql="SELECT * FROM user WHERE id = '".$q."'";
$result = mysqli_query($con,$sql);

echo "<table>
<tr>
<th>Firstname</th>
<th>Lastname</th>
<th>Age</th>
<th>Hometown</th>
<th>Job</th>
</tr>";
while($row = mysqli_fetch_array($result)) {
  echo "<tr>";
  echo "<td>" . $row['FirstName'] . "</td>";
  echo "<td>" . $row['LastName'] . "</td>";
  echo "<td>" . $row['Age'] . "</td>";
  echo "<td>" . $row['Hometown'] . "</td>";
  echo "<td>" . $row['Job'] . "</td>";
  echo "</tr>";
}
echo "</table>";
mysqli_close($con);
?>
</body>
</html>

AJAX and XML

<html>
<head>
<script>
function showCD(str) {
  if (str=="") {
    document.getElementById("txtHint").innerHTML="";
    return;
  }
  var xmlhttp=new XMLHttpRequest();
  xmlhttp.onreadystatechange=function() {
    if (this.readyState==4 && this.status==200) {
      document.getElementById("txtHint").innerHTML=this.responseText;
    }
  }
  xmlhttp.open("GET","getcd.php?q="+str,true);
  xmlhttp.send();
}
</script>
</head>
<body>

<form>
Select a CD:
<select name="cds" onchange="showCD(this.value)">
  <option value="">Select a CD:</option>
  <option value="Bob Dylan">Bob Dylan</option>
  <option value="Bee Gees">Bee Gees</option>
  <option value="Cat Stevens">Cat Stevens</option>
</select>
</form>
<div id="txtHint"><b>CD info will be listed here...</b></div>

</body>
</html>

<?php
$q=$_GET["q"];

$xmlDoc = new DOMDocument();
$xmlDoc->load("cd_catalog.xml");

$x=$xmlDoc->getElementsByTagName('ARTIST');

for ($i=0; $i<=$x->length-1; $i++) {
  //Process only element nodes
  if ($x->item($i)->nodeType==1) {
    if ($x->item($i)->childNodes->item(0)->nodeValue == $q) {
      $y=($x->item($i)->parentNode);
    }
  }
}

$cd=($y->childNodes);

for ($i=0;$i<$cd->length;$i++) {
  //Process only element nodes
  if ($cd->item($i)->nodeType==1) {
    echo("<b>" . $cd->item($i)->nodeName . ":</b> ");
    echo($cd->item($i)->childNodes->item(0)->nodeValue);
    echo("<br>");
  }
}
?>

AJAX Live Search

Live search has many benefits compared to traditional searching:

Results are shown as you type
Results narrow as you continue typing
If results become too narrow, remove characters to see a broader result

<html>
<head>
<script>
function showResult(str) {
  if (str.length==0) {
    document.getElementById("livesearch").innerHTML="";
    document.getElementById("livesearch").style.border="0px";
    return;
  }
  var xmlhttp=new XMLHttpRequest();
  xmlhttp.onreadystatechange=function() {
    if (this.readyState==4 && this.status==200) {
      document.getElementById("livesearch").innerHTML=this.responseText;
      document.getElementById("livesearch").style.border="1px solid #A5ACB2";
    }
  }
  xmlhttp.open("GET","livesearch.php?q="+str,true);
  xmlhttp.send();
}
</script>
</head>
<body>

<form>
<input type="text" size="30" onkeyup="showResult(this.value)">
<div id="livesearch"></div>
</form>

</body>
</html>

<?php
$xmlDoc=new DOMDocument();
$xmlDoc->load("links.xml");

$x=$xmlDoc->getElementsByTagName('link');

//get the q parameter from URL
$q=$_GET["q"];

//lookup all links from the xml file if length of q>0
if (strlen($q)>0) {
  $hint="";
  for($i=0; $i<($x->length); $i++) {
    $y=$x->item($i)->getElementsByTagName('title');
    $z=$x->item($i)->getElementsByTagName('url');
    if ($y->item(0)->nodeType==1) {
      //find a link matching the search text
      if (stristr($y->item(0)->childNodes->item(0)->nodeValue,$q)) {
        if ($hint=="") {
          $hint="<a href='" .
          $z->item(0)->childNodes->item(0)->nodeValue .
          "' target='_blank'>" .
          $y->item(0)->childNodes->item(0)->nodeValue . "</a>";
        } else {
          $hint=$hint . "<br /><a href='" .
          $z->item(0)->childNodes->item(0)->nodeValue .
          "' target='_blank'>" .
          $y->item(0)->childNodes->item(0)->nodeValue . "</a>";
        }
      }
    }
  }
}

// Set output to "no suggestion" if no hint was found
// or to the correct values
if ($hint=="") {
  $response="no suggestion";
} else {
  $response=$hint;
}

//output the response
echo $response;
?>

AJAX Poll

<html>
<head>
<script>
function getVote(int) {
  var xmlhttp=new XMLHttpRequest();
  xmlhttp.onreadystatechange=function() {
    if (this.readyState==4 && this.status==200) {
      document.getElementById("poll").innerHTML=this.responseText;
    }
  }
  xmlhttp.open("GET","poll_vote.php?vote="+int,true);
  xmlhttp.send();
}
</script>
</head>
<body>

<div id="poll">
<h3>Do you like PHP and AJAX so far?</h3>
<form>
Yes: <input type="radio" name="vote" value="0" onclick="getVote(this.value)"><br>
No: <input type="radio" name="vote" value="1" onclick="getVote(this.value)">
</form>
</div>

</body>
</html>

<?php
$vote = $_REQUEST['vote'];

//get content of textfile
$filename = "poll_result.txt";
$content = file($filename);

//put content in array
$array = explode("||", $content[0]);
$yes = $array[0];
$no = $array[1];

if ($vote == 0) {
  $yes = $yes + 1;
}
if ($vote == 1) {
  $no = $no + 1;
}

//insert votes to txt file
$insertvote = $yes."||".$no;
$fp = fopen($filename,"w");
fputs($fp,$insertvote);
fclose($fp);
?>

<h2>Result:</h2>
<table>
<tr>
<td>Yes:</td>
<td><img src="poll.gif"
width='<?php echo(100*round($yes/($no+$yes),2)); ?>'
height='20'>
<?php echo(100*round($yes/($no+$yes),2)); ?>%
</td>
</tr>
<tr>
<td>No:</td>
<td><img src="poll.gif"
width='<?php echo(100*round($no/($no+$yes),2)); ?>'
height='20'>
<?php echo(100*round($no/($no+$yes),2)); ?>%
</td>
</tr>
</table>

Remember to allow your web server to edit the text file. Do NOT give everyone access, just the web server (PHP).