PHP Example - AJAX Poll

AJAX Poll

The following example will demonstrate a poll where the result is shown without reloading.

Example Explained - The HTML Page

When a user chooses an option above, a function called "getVote()" is executed. The function is triggered by the "onclick" event:

< 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>

The getVote() function does the following:

• 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 (vote) is added to the URL (with the value of the yes or no option)

The PHP File

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

< ?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>

The value is sent from the JavaScript, and the following happens:

1. Get the content of the "poll_result.txt" file
2. Put the content of the file in variables and add one to the selected variable
3. Write the result to the "poll_result.txt" file
4. Output a graphical representation of the poll result

The Text File

The text file (poll_result.txt) is where we store the data from the poll.

It is stored like this:

0||0

The first number represents the "Yes" votes, the second number represents the "No" votes.

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