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Using AJAX to execute a PHP script through a JavaScript function

I have an anchor link with no destination, but it does have an onClick event:
<li><a href onClick='deletePost()'> Delete </a> </li>
I understand that I cannot directly execure PHP code blocks in JavaScript due to the nature of PHP and it being a server side language, so I have to utilize AJAX to do so.
When the delete link is clicked, I need it to execute this query (del_post.php)
<?php include("connect.php");
$delete_query = mysqli_query ($connect, "DELETE FROM user_thoughts WHERE id = 'id' ");
?>
I have tried to understand AJAX using similar past questions, but due to being relatively new, I cannot completely grasp it's language. Here is what I have tried:
function deletePost() {
xmlhttp=new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200){
xmlhttp.open("GET", "del_post.php", false);
xmlhttp.send();
}
}
}
But clicking the link just changes the URL to http://localhost/.

I believe the (main) problem is your empty "href" attribute. Remove that, or change it to href="#" or old school href="javascript:void()" (just remove it, imo).
It's been a while since I used XMLHttpRequest and not something like jQuery's .ajax, but I think you need to do it like so (mostly you need to .open/send before you watch for the state change):
var xmlHttpReq = new XMLHttpRequest();
if (xmlHttpReq) {
xmlHttpReq.open('GET', 'your-uri-here.php', true/false);
xmlHttpReq.onreadystatechange = function () {
if (xmlHttpReq.readyState == 4 && xmlHttpReq.status == 200) {
console.log('success! delete the post out of the DOM or some other response');
}
else {
console.log('there was a problem');
}
}
xmlHttpReq.send();
}

Can you please provide your : del_post.php file?
Normally you can show a text or alert in a
<div id="yourname"></div>
by using callback in an AJAX request :
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
document.getElementById("yourname").innerHTML = xmlhttp.responseText;
}
This response is coming from your PHP file for example :
function remove_record(ARG){
if ($condition==true)
echo "TRUE";
else
echo "FALSE";
}

You should remove href attribute from anchor tag and style the element with CSS.
Also, your script should look like this:
<script>
function deletePost() {
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (xhttp.readyState == 4 && xhttp.status == 200) {
// Do something if Ajax request was successful
}
};
xhttp.open("GET", "del_post.php", true);
xhttp.send();
}
</script>

You are trying to make the http request inside the callback.
You just need to move it outside:
function deletePost() {
var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
alert(xmlhttp.responseText);
}
}
xmlhttp.open("GET", "del_post.php", false);
xmlhttp.send();
}
Removing the href attribute will prevent the refresh. I believe that is valid in HTML5.

Ok... I'm just a hobbyist, so please forgive me any inaccuracies in the typing but this works: A format I use for an ajax call in an <a> element is:
<a href="javascript:" onclick="functionThatReallyCallsAjax()">
So that I have more flexibility(in case I need to check something before I send the ajax). Now, for an ajax call you need:
What file to call
What to do with the response from the file you called
What to do if an I/O error happens
So we have this function - not mine, leeched amongst thousands from somewhere - probably here :) - and probably well known, my apologies to the author, he is a genius: This is what you call for the ajax thing, where 'url' is the file you want to 'ajax', 'success' is the name of the function that deals with results and error is the name of the function that deals with IO errors.
function doAjaxThing(url, success, error) {
var req = false;
try{
// most browsers
req = new XMLHttpRequest();
} catch (e){
// IE
try{
req = new ActiveXObject("Msxml2.XMLHTTP");
} catch(e) {
// try an older version
try{
req = new ActiveXObject("Microsoft.XMLHTTP");
} catch(e) {
return false;
}
}
}
if (!req) return false;
if (typeof success != 'function') success = function () {};
if (typeof error!= 'function') error = function () {};
req.onreadystatechange = function(){
if(req.readyState == 4) {
return req.status === 200 ?
success(req.responseText) : error(req.status);
}
}
req.open("GET", url, true);
req.send(null);
return req;
}
You will naturally need to include the success+error functions:
function dealWithResponse(textFromURL)
{
//textFromURL is whatever, say, a PHP you called in the URL would 'echo'
}
function ohNo()
{
//stuff like URL not found, etc.
alert("I/O error");
}
And now that you're armed with that, this is how you compose the real call inside the function you called at the <a>:
function functionThatReallyCallsAjax()
{
//there are probably many scenarios but by having this extra function,
//you can perform any processing you might need before the call
doAjaxThing("serverFile.php",dealWithResponse,ohNo);
}
One scenario might be when you need to pass a variable to the PHP you didn't have before. In this case, the call would become:
doAjaxThing("serverFile.php?parameter1=dogsRock",dealWithResponse,ohNo);
And now not only you have PHP sending stuff to JS, you have JS sending to PHP too. Weeeee...
Final words: ajax is not a language, its a javascript 'trick'. You don't need to fully understand what the first 'doAjaxThing' function does to use this, just make sure you are calling it properly. It will automatically 'call' the 'deal WithResponse' function once the response from the server arrives. Notice that you can continue doing your business (asynchronous - process not time-tied) till the response arrives - which is when the 'deal WithResponse' gets triggered -, as opposed to having a page stop and wait (synchronous - time tied) until a response arrives. That is the magic of ajax (Asynchronous JAvascript and Xml).
In your case you want to add the echo("success") - or error! - in the PHP, so that the function 'dealWithResponse' knows what to do based on that info.
That's all I know about ajax. Hope this helps :)

How to pass ajax variable value to controller in codeigniter

Here i want to pass the 'q' value from ajax to controller function in codeigniter.
ajax code:
function getdata(str)
{
if (str == "") {
document.getElementById("yer").innerHTML = "";
return;
} else {
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("bus").innerHTML = xmlhttp.responseText;
}
}
xmlhttp.open("GET","<?php echo site_url('money_c/taxcalculator1'); ?>?q="+str,true);
xmlhttp.send();
window.location="<?php echo site_url('money_c/taxcalculator'); ?>"
}
}
controller:
function taxcalculator1()
{
$bt=$_GET['q'];
echo $bt;
}
Here i want to pass the 'q' value from ajax to controller function in codeigniter.

As soon as you have started the Ajax request sending with this:
xmlhttp.send();
You leave the page with this:
window.location="<?php echo site_url('money_c/taxcalculator'); ?>"
… which aborts the Ajax request, removes the place you are trying to edit with innerHTML and destroys the JavaScript that would be trying to do that anyway.
If you want to use Ajax then:
Put the data you want to show to the user the response from taxcalculator1
Use onreadystatechange to show it to the user
Don't leave the page before that happens (remove the window.location line).
If you want to load an entirely new page:
Don't use Ajax
Just submit a form to a URL
Display the data you want the user to see (in the form of an HTML document) in the response to that request

How to load data from an XML file using php to show it in an html page with javascript

I'm doing an assigment for my programming class. I need to show a table with two columns (name and lastname) of a list of friends. This data is stored in a XML file like this:
<?xml version='1.0' standalone='yes'?>
<amigos>
<amigo>
<nombre>Alejandra</nombre>
<apellido>Ponce</apellido>
</amigo>
<amigo>
<nombre>Dalia</nombre>
<apellido>Gordon</apellido>
</amigo>
I retrieve this data with php, like this:
<table width="200" border="1">
<tr align="center">
<td>NOMBRE</td>
<td>APELLIDO</td>
</tr>
<?php
$amigos = simplexml_load_file('listaamigos.xml');
foreach ($amigos->amigo as $amigo) {
echo '<tr>';
echo '<td>',$amigo->nombre,'</td>';
echo '<td>',$amigo->apellido,'</td>';
echo '</tr>';
}
?>
I call this php file with a function written in javascript language. I'm using ajax for this homework. My javascript file is the one I'm showing below:
var xmlHttp;
function createXmlHttpRequestObject() {
if(window.ActiveXObject){
try{
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
}catch(e)
{
xmlHttp=false;
}
}
else{
try{
xmlHttp = new XMLHttpRequest();
}catch(e)
{
xmlHttp=false;
}
}
if(!xmlHttp)
alert('Can't connect to the host');
else
return xmlHttp;
}
function cargarAmigos(url)
{
if(url=='')
{
return;
}
xmlHttp=createXmlHttpRequestObject();
xmlHttp.open("GET", url, true);
xmlHttp.onreadystatechange = procesarEventos;
xmlHttp.send(null);
}
function cargar(url)
{
if(url=='')
{
return;
}
xmlHttp=createXmlHttpRequestObject();
xmlHttp.open("GET", url, true);
xmlHttp.onreadystatechange = procesarEventos;
xmlHttp.send(null);
}
function procesarEventos()
{
if(xmlHttp.readyState == 4)
{
document.getElementById("listaAmigos").innerHTML= xmlHttp.responseText;
}
}
I use this javascript file in a html file. I call the function cargar () in the button's onclick event, like this:
<body>
<div id="listaAmigos" >
Lista amigos
</div>
<button onclick="cargarAmigos('procedimiento.php');">Lista Amigos Ajax</button>
</body>
The problem is that the code is not working. I mean that the names are not displaying at all in the table. Actually the table does not appear.
I'm pretty sure that the error is not in the code because it was working last week and I haven't changed the code since then. But today I loaded the html page just for "fun" and it wasn't showing my list of friends.
So I decided to open another project with uses the same algorithm and this one is not working too. I've checked that all the files are in the same folder. I've checked my xammp server and it's apache and mysql services are on. I have no idea what "thing" I could have done to cause this problem.
Any help will be really appreciated.

It looks like you should escape the ' character in this line:
alert('Can't connect to the host');
i.e. rewrite it like
alert("Can't connect to the host");
You can see that there's an error even just by looking at the formatting on Stack Overflow :)
Please refer to this question for the details on why it's working like that: When to use double or single quotes in JavaScript?

Replacing content using AJAX when clicking a link

I want to use AJAX to replace the contents of a div. Although the application is fairly complex, I have tried to dumb it down in isolation so that I can get the basic concept working first.
For now, I just want to replace a div as per the PHP file...
<?php
$id = $_GET['id'];
if ($id = 1)
{
$text = 'This is some text';
}
elseif ($id = 2) {
{
$text = 'This is a lot more text than the first text!';
}
elseif ($id = 3) {
{
$text = 'This is a lot more text than the first text, and a load more than the third as well!!';
}
echo $text;
?>
Fairly simple stuff really. So here's my HTML file...
<!DOCTYPE html>
<html>
<head>
<script>
function loadXMLDoc()
{
var xmlhttp;
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("myDiv").innerHTML=xmlhttp.responseText;
}
}
xmlhttp.open("GET","ajax.php",true);
xmlhttp.send();
}
</script>
</head>
<body>
<div id="myDiv">I want this content replacing</div>
ID: 1<br>
ID: 2<br>
ID: 3
</body>
</html>
I realise what is there will never work as I've modified some stuff I found online, but basically I'm looking to pass a variable such as the ID in the link to the AJAX script to replace the contents of the div.
How do I get this working? Is there a better alternative to using <a> tags?

Using jQuery
Your HTML
ID: 1
Javascript
// Delegate click event
$(document).on('click', 'a.ajax', function(){
var el = $(this);
$.ajax({
url: 'ajax.php',
data: {id: el.data('id')},
}).done(function(response){
$('#myDiv').html(response);
});
return false;
});

I'll answer your question using Vanilla JavaScript rather than using the jQuery AJAX Helper. Although it's very good - but learning the Vanilla way will give you a good idea of what the libraries do to aid you.
Firstly, you are making an Ajax call but albeit, an Empty one.
"Query" parameters is what $_GET is based on, are formated like:
?Key=Value&KeyTwo=SomeOtherValue
Which in PHP, Translates too:
Array
(
[Key] => Value
[KeyTwo] => SomeOtherValue
)
This'll need to be passed along with the xmlhttp.send() for it to make an successful ajax call, with Data.
But to collect this data in the first place, you must collect it with your HTML:
<!-- Notice how the <a> tags now have attributes attached, the id="" -->
ID: 1<br />
ID: 2
<script>
function loadXMLDoc( Id ) {
/**
* Id is the <a href="#" id="3" collected
* when onclick="loadXMLDoc()" is pressed
**/
var xmlhttp,
DataId = Id.attributes.id.value;
if (window.XMLHttpRequest)
xmlhttp = new XMLHttpRequest();
else
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200)
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
}
/**
* Notice the ?id="+ dataId +"
* It's passing through the ID Collected
**/
xmlhttp.open("GET","ajax.php?id="+ dataId +"",true);
xmlhttp.send();
}
</script>
Although this code above is very inefficient, you would be much better in JavaScript & Programming in general to keep things generic. By modifying your code to:
ID: 1<br />
ID: 2
<script>
function getId() {
alert( this.attributes.id.value );
//Click on id="2", alerts '2'
}
/**
* We find all the HTML tags with the
* attribute that has 'class="idlistener"
* attached, we 'bind' it to a function called
* getId()
**/
var IdListener = document.getElementsByClassName('idlistener');
for( var x = 0; x < IdListener.length; x++ ) {
IdListener[x].addEventListener( 'click', getId, false );
}
</script>
Demo: Fiddle
Lastly, It does look to me you've discovered this AJAX Code from W3Schools.com. I think you'll find every StackOverflow Web Developer that would agree with me - Don't learn from this Site!

General format for replacing html content with the response from an ajax call:
$.ajax({
url: yourUrl,
method: 'get', // or 'post'
success: function (response) {
$('#myDiv').html(response);
}
// other ajax options here if you need them
});

You dont need to use ajax for that. Just use the following in the condition. Dont forget to call the jquery js file on the header. Otherwise jquery wont work:
echo '<script>$("#myDiv").html("This is some text")</script>';

Ajax resending XMLHttpRequest

I've got a client side js/ajax script like this:
<p>server time is: <strong id="stime">Please wait...</strong></p>
<script>
function updateAjax() {
xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState==3 && xmlhttp.status==200) {
document.getElementById("stime").innerHTML=
xmlhttp.responseText;
}
if (xmlhttp.readyState==4) {
xmlhttp.open("GET","date-sleep.php",true);
xmlhttp.send();
}
}
xmlhttp.open("GET","date-sleep.php",true);
xmlhttp.send();
}
window.setTimeout("updateAjax();",100);
</script>
And a on the server side:
<?php
echo 6;
for ($i=0; $i<10; $i++) {
echo $i;
ob_flush(); flush();
sleep(1);
}
?>
After first 'open' and 'send' it works ok, but when the server finishes the script and xmlhttp.readyState == 4 then the xmlhttp resends the request but nothing happens.

Instead of re-using the same XHR object all the time, try repeating the function with a new object. This should at least fix incompatibility issues as you listed.
Try re-calling your Ajax function inside the callback of it, if you want to loop it infinitely.
if (xmlhttp.readyState==4) {
updateAjax(); //or setTimeout("updateAjax();",100); if you want a delay
}
I'd also suggest putting your .innerHTML method inside the .readyState==4, which is when the requested document has completely loaded, and .status==200 which means success. Like this:
if (xmlhttp.readyState==4 && xmlhttp.status==200) {
document.getElementById("stime").innerHTML=
xmlhttp.responseText;
updateAjax(); //or setTimeout("updateAjax();",100);
}
Also, if you want your Ajax to be cross-browser, you should test if the browser supports the XHR object which you're using:
var xmlhttp = (window.XMLHttpRequest) ? new XMLHttpRequest() : new ActiveXObject("Microsoft.XMLHTTP");
I just typed the code above but it should work just fine to add compatibility with older versions of IE and other browsers.