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how php and javascript communicate specifically with this code

I'm trying to write a php and javascript code that's going to behave similarly to the code I have below (I didn't write the code) but I'm a little confused on what's going on in the php and how the two are communicating. I've tried to watch videos and read about php but I'm still pretty confused by it.
Then the javascript makes requests to the php when its buttons are clicked and the php sends information back.
The general function of the php file is it displays the contents of a random file in the http://webster.cs.washington.edu/cse154/services/flashcards/pokemon directory. It can take in a parameter called mode. When the user passes in a mode value of categories it outputs a list of all of the folder names in http://webster.cs.washington.edu/cse154/services/flashcards. Otherwise, it just displays the contents of a random file as before.
I get it on a broad overview but I'm still kind of confused on how the php code is working. Like I said I'm trying to write a code that's going to be quite similar to this so I just am trying to get a better understanding of how php works but all the information i've read hasn't been that helpful.
<?php
# Solution to CSE 154 Flashcard lab.
# generates a JSON list of categories if passed a parameter mode
# with the value of categories. Otherwise outputs a random question
# from the passed in category in XML.
$mode = $_GET["mode"];
$category = $_GET["category"];
$url = "../../cse154/services/flashcards/";
if($mode == "categories") {
outputJson($url);
} else {
outputXml($url, $category);
}
# outputs the list of available categories in JSON
function outputJson($url) {
$files = glob($url . "*");
$json = array("categories" => array());
foreach($files as $file) {
$count = count(glob($file."/*"));
$json["categories"][basename($file)] = $count;
}
header("Content-type: application/json");
print(json_encode($json));
}
# outputs a random question about the provided category in XML
function outputXml($url, $category) {
$files = glob($url . "$category/*");
$index = array_rand($files);
// this is a great place to use list!!
list($ques, $ans) = file($files[$index]);
$dom = new DOMDocument();
$card = $dom->createElement("card");
$dom->appendChild($card);
$question = $dom->createElement("question");
$question->appendChild($dom->createTextNode($ques));
$card->appendChild($question);
$answer = $dom->createElement("answer");
$answer->appendChild($dom->createTextNode($ans));
$card->appendChild($answer);
header("Content-type: text/xml");
print($dom->saveXML());
}
?>
/* javascript */
(function() {
var category = "computerscience";
var xml = null;
// sets up onclick handlers
window.onload = function() {
document.getElementById("viewAll").onclick = viewAll;
document.getElementById("next").onclick = next;
};
// sends an ajax request to the passed in address.
// calls the passed in function when the request returns.
function ajax($adress, $function) {
var request = new XMLHttpRequest();
request.onload = $function;
request.open("GET", $adress, true);
request.send();
}
// makes a request for all of the categories.
function viewAll() {
ajax("flashcards.php?mode=categories", displayAll);
}
// displays all categories in a list on the page.
function displayAll() {
$json = JSON.parse(this.responseText);
for($cat in $json.categories) {
var li = document.createElement("li");
li.innerHTML = $cat;
li.onclick = choose;
document.getElementById("categories").appendChild(li);
}
}
// sets a new category as the category all questions should come from.
function choose() {
category = this.innerHTML;
}
// displays the next question if it was last displaying an answer or nothing.
// displays the answer to the previous question otherwise.
function next() {
if(!xml) {
ajax("flashcards.php?category=" + category, displayNext);
} else {
document.getElementById("card").innerHTML = xml.querySelector("answer").textContent;
xml = null;
}
}
// displays the question that it recieved from the server.
function displayNext() {
xml = this.responseXML;
document.getElementById("card").innerHTML = xml.querySelector("question").textContent;
}
})();

How to implements Progress bar when doing Ajax request Voluminous db updates

Good morning,
I have script that updates voluminous data (for exemple 3000Lines) and I have to show to user progress of db updates on progress bar or just the number of lines affected.
I'm working on PHP codeigniter and AJAX
I had an idea to use session codeigniter to store modified variable (incrementation) on the session value on each Loop and call function that give me the session variable as JSON array, but the problem is that the session wouldn't change itself after first update (for exemple: starting with 0 and modified to 20, after that all process on 20)
I don't know how to get better solution to do it. If you can help me it will be really cool.
Thank's to all

PHP won't output anything until the script has fully completed, but you can change that:
ob_implicit_flush(true);
for ($i = 0; $i < ob_get_level(); $i++) {
ob_end_clean();
}
Put this in your PHP script before you start processing your data. As you process parts of your data, output something to tell the AJAX request the progress; for example:
PHP:
$completed_updates = 0;
$last_echoed_progress = 0;
$progress_echo_interval_seconds = 2;
while ($completed_updates < $amount_of_db_updates_to_do) {
do_db_update();
$completed_updates++;
if ($last_echoed_progress + $progress_echo_interval_seconds < time()) {
echo ($completed_updates / $amount_of_db_updates_to_do) * 100;
$last_echoed_progress = time();
}
}
jQuery's .ajax also (by default) won't call the success function with the data until all the data has been received (i.e. script ended), so create a custom XHR object with an event listener that receives the data while the script is still running:
JS:
var last_response_length = 0;
$.ajax({
... // All your other settings
xhr: function() {
var xhr = new XMLHttpRequest(); // Create a custom XHR object
xhr.onprogress = function(data) {
var response = data.currentTarget.response, // Get the output
progress = response.slice(last_response_length) | 0; // Remove old output
$( '#progress-bar' ).val(progress); // Update the progress bar
last_response_length = response.length; // Track where the old data is (so they can be removed when new data is received)
};
return xhr; // IMPORTANT! Return the custom XHR for .ajax to use
},
success: function(response) {
$( '#progress-bar' ).val(100); // All done!
}
});
Obviously modify the code to suit your needs, and experiment a little. Keep in mind that PHP has an execution time limit of 30 seconds by default, so you may need to change this inside your script:
set_time_limit(0);
This allows your script (and only that one) to run without time limits. Put it at the very top. Use caution!

Returning JSON from PHP, convert JSON to javascript array, return array from AJAX call

I am working on a project that uses a function I called AjaxRequest which handles all AJAX requests I make. I have no problems in making the request however getting the request back is the issue and placing it where I want it on my page is becoming stressful.
HTML BIT
<body onLoad="calling();">
<div id="status">Status: </div>
</body>
JAVASCRIPT BIT
function calling() {
var answer = ajaxRequest("testing", "test.php", "test=test");
document.getElementById("status").innerHTML += answer[1];
document.getElementById("status").innerHTML += " " + answer[3];
}
function ajaxRequest(app, location, credentials) {
var extras = "";
if(credentials === "" || credentials) {
extras = "&" + credentials;
}
var ajax = ajaxObj("POST", location);
ajax.onreadystatechange = function() {
if(ajaxReturn(ajax) == true) {
var obj = JSON.parse(ajax.responseText);
var arrayObj = [];
for(var i in obj) { arrayObj.push([i, obj[i]]); }
return arrayObj;
}
}
ajax.send("app=" + app + extras);
}
there are two other functions running: ajaxObj and ajaxReturn but I excluded those because they is not the problem. Furthermore, I am trying to make ajaxRequest an efficient function that could be used by more than one application without having to rewrite all the code in more than one location. All error handling acquires before the actual use of ajaxRequest.
PHP BIT
<?php
if($_POST['app'] == "testing") {
$hey = array('success' => 1, 'message' => 'Successful');
echo json_encode($hey);
exit();
}
?>
I'm using calling as a javascript function that does all error handling, this is just basic for the whole of my project however I try to get the JSON from php and convert it to array and the issue is returning the array into calling. I try to display the information on the page yet nothing works.
I am not looking to use any JQuery for my project so I would like to exclude the use of it for this piece of code.

If you want, you could set the header before sending back the json.
header('Content-Type: application/json');
Usually you don't need it, but it will tell your javascript that it's json, and the array will be transform in a javascript object. It work with Jquery, but I assume it'll work without too

Retrieving a specific link from url using javascript

I need to make a function in JavaScript to locate href inside the url that is given, and to return it as a string.
For example: http://stackoverflow.com/
So the function starts with: function example(url) {}
I want to find the first link inside this url that contain the words google.
In this page there is somewhere link like <a href:"http://google.com/asdasdadsa/asdada">
The function is to return the whole link as string.

So basically from what I can gather, you want to look at each link on the page and get the whole URL if it includes some string (i.e. google).
Here's a function that finds the first link matching a certain string:
function checkLinks( searchString ) {
var url;
// Go through each link
$('a').each( function ( ) {
// Check if the search string exists
if( $(this).attr('href').indexOf(searchString) != -1 ) {
url = $(this).attr('href');
// If we've found one, stop the each.
return false;
}
});
return url;
}
I've put together a jsfiddle showing an example of how this function could be used:
http://jsfiddle.net/K9KvS/1/
EDIT:
I've just seen you need to do this on a remote URL. You probably need to use AJAX to load in the code, then run this on the code you have. Unfortunately due to the same origin policy, you can't get this directly, so you'll need to run a server-side script on your server (e.g. using PHP) to load the content of the external page, then an AJAX call from your JS to pull it into your javascript.
Modified version to include an AJAX load of some code, then a find on that code:
// Create a function to do the actual search
function checkLinks( code, searchString ) {
var url;
// Search the code for all <a> tags, the loop over them
$(code).find('a').each( function ( ) {
// Check if there is a match (indexOf returns -1 if not)
if( $(this).attr('href').indexOf(searchString) != -1 ) {
// set the "url" variable to the href
url = $(this).attr('href');
// Stop looping
return false;
}
});
return url;
}
// Now, when the page loads, attach an AJAX call to a button with ID "linkchecker"
$( function ( ) {
$('#linkchecker').click( function( ) {
var code;
// Perform the AJAX call, load the data and call our function above to find "google.com"
$.get( 'load_code.php?url=http://www.google.com', function( data ) {
code = data;
alert( checkLinks( code, 'google.com' ) );
});
});
});
load_code.php would probably look something like this (probably with some error checking, etc):
<?php
$htm = file_get_contents($_GET['url']);
echo $htm;
?>
Update: Using Raw Javascript
We'll modify checkLinks from above to use raw Javascript:
function checkLinks( code, searchString )
{
var url;
// We need to create an HTML document element so we can use javascript dom functions on it.
var doc = document.createElement("html");
doc.innerHTML = code; // put the code into the document
// Get all links in the code
var links = doc.getElementsByTagName("a")
// Loop over all links
for (var i=0; i<links.length; i++) {
// Check if the search string (e.g "google.com") is found in the href of the link
if( links[i].getAttribute("href").indexOf(searchString) != -1 ) {
// Set it to the return value
url = links[i].getAttribute("href");
// stop looping
break;
}
}
return url;
}
So firstly, you need to set up the Ajax request object. The problem is this differs between browsers, so you need an unpleasant bit of code to generate it across them. The following is modified from the tiztag ajax tutorial:
function makeAJAXObject(){
var ajaxRequest; // The variable that makes Ajax possible!
try{
// Opera 8.0+, Firefox, Safari
ajaxRequest = new XMLHttpRequest();
} catch (e){
// Internet Explorer Browsers
try{
ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try{
ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e){
// Something went wrong
alert("Your browser broke!");
return false;
}
}
}
return ajaxRequest;
}
Ok, so now we've got our AJAX object, we want to get it to load a page, and tell it how to handle what we get back:
/*
* A function to load a given URL and process the code from it.
* It takes three arguments:
* php_handler The name of the PHP file that will load the code (or ASP, or whatever you choose to use)
* url The URL to be loaded.
* searchString The string to find in the links (e.g. "google.com").
*/
function load_page( php_handler, url, searchString )
{
// Get the ajax object using our function above.
window.ajax = makeAJAXObject( );
// Tell the AJAX object what to do when it's loaded the page
window.ajax.onreadystatechange = function(){
if(window.ajax.readyState == 4){ // 4 means it's loaded ok.
// For simplicity, I'll just alert this, but you would put your code to handle what to do when a match is found here.
alert(checkLinks( window.ajax.responseText, searchString ));
}
}
// Set up the variables you want to sent to your PHP page (namely, the URL of the page to load)
var queryString = "?url=" + url;
// Load the PHP script that opens the page
window.ajax.open("GET", php_handler + queryString, true);
window.ajax.send(null);
}
The final thing is to attach this to a button when the page has loaded:
window.onload = function( ) {
document.getElementById('linkchecker').onclick = function( ) {
load_page('load_page.php', 'http://www.example.com', 'google');
}
}
Please note, there's likely to be built in WinJS functions to handle some of the AJAX stuff, but I've never tried Win 8 app development, so I don't know them!

Help me properly make an AJAX call

I have a JavaScript function that is being called. I need to have it call a PHP function and return a true/false.
The script with the function is in the file /db/cancel_hike.php
My current JS looks like this:
function uncancelHike( hike_id )
{
//var url = "/db/cancel_hike.php;
var success = null;
var request = window.ActiveXObject ?
new ActiveXObject('Microsoft.XMLHTTP') :
new XMLHttpRequest;
request.open("GET", url , true);
request.onreadystatechange = function()
{
if (request.readyState == 4)
{
var xmlDoc = request.responseXML;
// obtain the array of markers and loop through it
markers = xmlDoc.documentElement.getElementsByTagName("marker");
for (var i = 0; i < markers.length; i++)
{
// obtain the attribues of each marker
success = markers[i].getAttribute("success");
if ( success == "true" )
{
document.getElementById("success").style.display = 'block';
document.getElementById("warning").style.display = 'none';
document.getElementById("error").style.display = 'error';
}
if ( success == "false" )
{
document.getElementById("success").style.display = 'none';
document.getElementById("warning").style.display = 'none';
document.getElementById("error").style.display = 'block';
}
}
}
}
request.send(null);
return false;
}
What I am having trouble with is:
How to call an actual function in the PHP script?
Do I absolutely need to have some XML returned? Or is there a way to just get back the returned value?
I am using YUI JS library. Do I need to make some calls to it, or is it not necessary in this case?

How to call an actual function in the PHP script?
You can't. You request URIs.
Write a PHP script that calls the function you want and place it at the URI you call.
(You can use query strings and the like as the input to an if statement that you use to conditionally call different functions)
Do I absolutely need to have some XML returned? Or is there a way to just get back the returned value?
You can return any kind of data you like.
I am using YUI JS library. Do I need to make some calls to it, or is it not necessary in this case?
It's a library. You never need to make calls to it. It often simplifies the code you have to write.

How to call an actual function in the PHP script?
Do I absolutely need to have some XML returned? Or is there a way to just get back the returned value?
Well, you don't call the actual function. What you want to do is pass variables using GET, that is, by appending them to the URL like file_name.php?var1=this&var2=that to pass var1 of "this" and var2 equaling "that." You retrieve them in the PHP file with $_GET['this'] and $_GET['that']. Whatever PHP outputs to the page via echo, print_r, etc. is then sent back in a request object as part of its responseText property.
You just set url in request.open to a URL on your site. For example, in your .js file:
request.open("GET", "answer_me.php?hike_id=" + hike_id, true);
And in your .php file:
<?php
$hike_id = $_GET['hike_id'];
if ($hike_id < 5) {
echo "true"; // echo true would return "1", BTW
} else {
echo "false"; // echo false would return nothing
}
Note that that will just return a string value to request.responseText of false, thus you could do this:
var result = request.responseText;
if (result === "true") {
...
document.getElementById("success").style.display = "block";
...
} else {
...
document.getElementById("success").style.display = "none";
...
}
You do not need it to be XML, especially as it looks like you're not really using the loop (the same three DOM elements are being assigned values each time).
And honestly, for AJAX I'd recommend using a framework like jQuery (or YUI, although I don't find its AJAX stuff as intuitive). Your entire code would look like this:
var $success = $("#success");
var $error = $("#error");
function cancelHikeCallback(data) {
var is_success = (data === "true");
$success.toggle(is_success);
$error.toggle(!is_success);
}
function cancelHike(hikeIdToSend) {
$.get("/db/cancel_hike.php", {hike_id: hikeIdToSend}, cancelHikeCallback);
}
IMO things like jQuery's $.ajax ($.get is a specialized form of $.ajax) make this stuff much easier to read and debug.
jsFiddle Example