Develop Reference

XMLHttpRequest does not seem to do anything

i have been trying very unsuccessfully to download a binary file from my server using jquery-ajax, which i finally gave up. so now i am trying to use XMLHttpRequest instead. however, i cannot even get a simple example working.
strangely enough, this code does not appear to do anything. i copy/pasted this from w3schools and this example is near identical to many other examples. it does not work for me in either chrome or FF:
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (xhttp.readyState == 4 && xhttp.status == 200) {
// Action to be performed when the document is read;
}
};
xhttp.open("GET", '/blah/blah/output.png', true);
xhttp.send();
we go into the onreadystatechange function only once, on the open() statement with an xhttp.readyState equal to one, but not on the send() step. i should think it would at least throw some kind of error rather than do nothing at all.
also, as an experiment, i purposely fed the open() a bad url - but again no reply.
can anybody tell me what i might be doing wrong?
thank you very much.

Your code looks correct to me, which points to some external cause.
Is your code flowing all the way through to the end of the execution context? Browsers will hold onto network requests until the engine yields back to the browser.
For instance:
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (xhttp.readyState == 4 && xhttp.status == 200) {
// Action to be performed when the document is read;
}
};
xhttp.open("GET", '/blah/blah/output.png', true);
xhttp.send();
while(true){}
will never send the call.

XML HTTP GET Request Fails

I'm doing a pure JS GET request, to my localhost (don't worry I tested POST and that works), I can access all the database and everything else but the GET request won't work. My JS code is shown below:
functtion getSessionKey() {
XMLHTTP = new XMLHttpRequest();
XMLHTTP.open("GET", "http://127.0.0.1:8080/projects/To-Do-App/api/sessionData/sessionKey.php", true);
XMLHTTP.onreadystatechange = function () {
if (XMLHTTP.readyState == 4) {
alert(XMLHTTP.responseText);
}
}
XMLHTTP.send(null);
}
In the PHP file I have the following code:
<?php
session_start();
if (isset($_SESSION['sessionKey']) && !empty(trim($_SESSION['sessionKey']))) {
echo htmlspecialchars(trim($_SESSION['sessionKey']));
}
?>
The POST requests all work and insert into the database, but the GET request seem to stop all the JS code below it from working. Any ideas why? I have tried changing the last parameter true/false. Also I am trying to make it for a mobile application through Intel XDK so I using JS and PHP if that helps. Please no jQuery solutions as that doesn't seem to work.

You didn't set the content type
var XMLHTTP = new XMLHttpRequest();
XMLHTTP.setRequestHeader("Content-type","application/x-www-form-urlencoded");
...
and try to replace
XMLHTTP.send(null);
with
XMLHTTP.send();

Don't send a null in with the .send() Make it
XMLHttp.send()

Function delivers value, before ajax request changed it

I am running an ajax request to retrieve a value of either 0,1, or 2 based upon some mysql code in the "check_answer_status.php" file. For test purposes, I have included the alert to check whether the general ajax and mysql request works fine and it does, hence the value contained within "Questiions.answerStatus" at the time of the alert is correct. However, my problem is that the function "checkAnswerStatus" has already executed and did not change the inital value of "answerStatus" (which I set to 50 for test purposes).
Context: sometime later in the code I want to execute code dependent on the value of the variable "answerStatus".
I believe I need to somehow include something like an "oncomplete" or something comparable, but I do not know how to do that. Can anyone help me out? Many thanks!
var = Questions = {
answerStatus:50,
checkAnswerStatus : function(question){
var xmlhttp;
if (window.XMLHttpRequest){
xmlhttp=new XMLHttpRequest();
}
xmlhttp.onreadystatechange=function(){
if (xmlhttp.readyState==4 && xmlhttp.status==200){
test = xmlhttp.responseText;
Questions.answerStatus = test;
alert(Questions.answerStatus);
}
}
xmlhttp.open("POST","../../include/check_answer_status.php",true);
xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
xmlhttp.send("q="+question);
},

The request you make is asynchronus (the third parameter of the xmlhttp.open function). If you changed it to:
xmlhttp.open("POST","../../include/check_answer_status.php",false);
it should work.
Another options is to pass a callback to your checkAnswerStatus function, and call the callback when the request finishes. Example:
checkAnswerStatus : function(question, callback){
var xmlhttp;
if (window.XMLHttpRequest){
xmlhttp=new XMLHttpRequest();
}
xmlhttp.onreadystatechange=function(){
if (xmlhttp.readyState==4 && xmlhttp.status==200){
test = xmlhttp.responseText;
Questions.answerStatus = test;
callback(Questions.answerStatus); //call the function
}
}
xmlhttp.open("POST","../../include/check_answer_status.php",true);
xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
xmlhttp.send("q="+question);
}
and then you will call the function like this:
Questions.checkAnswerStatus("bla bla", function(answerStatus) {
alert(answerStatus);
});

in addition to Nemos answer I would recommend you read following resources from MDN:
More technical API documentation for a brief overview of all the possibilities:
https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest
More real life usecases:
https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Using_XMLHttpRequest
Hope this helps

Execute <script> from separate .php file

Been working on (what seemed like) a simple issues for a few days now and could use some help.
I call a php file on a button-click, do a bunch of server-side operations, and wish to change a few things in the HTML at the end of the php (change images, changing text, enabling buttons, etc.)
So, what I'm trying to do (for the test case here) is change an image twice. It works fine in the first set of code (script in the html file), but it doesn't work in the second set of code (script in the php file). I.e., I see oldImage when the page loads, secondImage when I click the button, but I never see newImage.
<button onclick="test()">Try The Test</button>
<img id="myImage" src="oldImage.jpg">
<script>
function test()
{
var img = document.getElementById('myImage');
img.src = 'secondImage.jpg';
xmlhttp=new XMLHttpRequest();
xmlhttp.open("testPhp.php",true);
xmlhttp.send();
}
</script>
Here's myPhp.php (all on one line in my code; two lines here, for readability):
$script = "<script> var img = document.getElementById('myImage');
img.src = 'newImage.jpg'; </script?";
echo $script;
Any ideas on why the script in myPhp.php doesn't work?
EDIT:
I changed the HTML portion to this, then changed myPhp.php to echo "Hello World", which shows up just fine within myDiv. However, I can't seem to echo the script. Is there any way to do this?
xmlhttp=new XMLHttpRequest();
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
}
}
xmlhttp.open("GET","portTester.php",true);
xmlhttp.send();

If your ajax call returns markup, for it to have any effect, it has to be added to the DOM.
But I wouldn't recommend doing it this way. Instead, have your PHP file return the information (not a script), and then have the code receiving the information (in the onreadystatechange handler of the XHR object) read that information and take the relevant action.
For example, your PHP could simply return:
newImage.jpg
Then your ajax call would be:
function test()
{
var img = document.getElementById('myImage');
img.src = 'secondImage.jpg';
xmlhttp=new XMLHttpRequest();
xmlhttp.onreadystatechange = handleReadyStateChange;
xmlhttp.open("testPhp.php",true);
xmlhttp.send();
function handleReadyStateChange() {
if (xmlhttp.readyState === 4 && xmlhttp.status >= 200 && xmlhttp.status < 400) {
// Request is complete and successful
img.src = xmlhttp.responseText;
}
}
}
If you need to send back richer information (as is frequently the case), look at using JSON.

You're not doing anything with the response to your AJAX call. In other words: You are calling the PHP script, the reply is printed, but is thrown away, because your Javascript isn't doing anything with it. You must add some code to interact with the reply. Here's a hint: Don't try to output Javascript from PHP, output something that you USE in your Javascript.
Add this to your Javascript after the xmlhttp.send() call:
xmlhttp.onreadystatechange=function() {
if (xmlhttp.readyState==4 && xmlhttp.status==200) {
document.getElementById("myImage").src = xmlhttp.responseText;
}
}
And in your PHP script, put just this:
echo 'newImage.jpg';

One possible issue is that you are missing the semi-colon after your test() in the onclick. Also, your </script> tag is malformed; it reads </script? while it should read </script>. Also, where into the DOM is this echoing? It should go into the head of your document. Right now, it looked unspecified.

Javascript security stopping me?

I'm pretty sure it's a security issue keeping me from doing this, but I wonder if there's a workaround I don't know of...
I have a script to inject a user's email into the contact DB of my client and it's bombing in IE but working in FF, Chrome (as usual). Just wondering if I can add the server to the trust or something to make it work?
<script type="text/javascript">
window.onload = init;
//Global XMLHTTP Request object
var XmlHttp;
function CreateXmlHttp() {
//Creating object of XMLHTTP in IE
try {
XmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e) {
try {
XmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
}
catch (ex) {
XmlHttp = null;
}
}
//Creating object of XMLHTTP in Mozilla and Safari
if (!XmlHttp && typeof XMLHttpRequest != "undefined") {
XmlHttp = new XMLHttpRequest();
}
}
function init() {
var x = document.getElementsByName("btnContinue");
x[0].onclick = submitForm;
}
function submitForm() {
var x = document.getElementsByName('Email');
if (x[0].value.length > 0) {
CreateXmlHttp();
XmlHttp.open("POST", "https://app.icontact.com/icp/signup.php", false);
XmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
XmlHttp.send("redirect='http://www.xyz.com/articles.asp?ID=97'&errorredirect='http://www.xyz.com/articles.asp?ID=256'&fields_email=" +
x[0].value + "&listid=123&specialid:123=YP7I&clientid=123&formid=123&reallistid=1&doubleopt=0&Submit=Submit");
}
}
</script>
I'd appreciate any insight.
Thanks!

My first suggestion would be to try creating XMLHttpRequest before ActiveX Objects. IE7 and up DO support AJAX the way other browsers do.
Next, you should use relative paths in the open() method. Although I think form your question it's something that'll need to be able to run on any site? In that case I'd suggest creating a form and an iframe and using the "old" method.

It is a same-origin policy issue. The allow access content headers may be set, but the IE ActiveXObject won't use them. XMLHttpRequests obey the headers and will work on browsers that support them.
See this question:
AJAX Permission Denied On IE?
Though it doesn't look like they found a solution for an IE compatible cross-domain POST...
If you could proxy it through your web server (Make a POST to your server), and have the server make the POST, your problem would be solved.

On new browsers, you can use cross-domain XHR if you can have a special HTTP header on the page you request.
http://ejohn.org/blog/cross-site-xmlhttprequest/
Or you can use dynamic script loading.