I want to make it such that an image on a website gets its "onclick" event disabled and a gray filter applied, if a certain file on the same domain is not found. I want to use purely JS and have tried this so far:
function fileNonExist(url, callback){
var http = new XMLHttpRequest();
http.onreadystatechange = function() {
if (http.readyState === XMLHttpRequest.DONE && callback) {
if(http.status != 200){
callback();
}
}
}
http.open('HEAD', url);
http.send();
}
fileNonExist("theFileIAmLookingFor.html", () => {
console.log("image changed");
image.onclick = "";
image.style.filter = "grayscale(100%)";
});
I have the image initialized and displayed. Thus image.onclick = "" and image.style.filter = "grayscale(100%)
both work, if they are used normally. However, even though the function blocks are executed as intended (Console logs "image changed" if the file isnt found, and nothing otherwise.) none of the style changes are ever visible, if they are executed from within those blocks. Why might that be and how could I fix it?
I found out the solution myself, while talking to Emiel Zuurbier: I noticed that the code works if I open the html file normally in my browser. The bug occurs, if I access the file over a webserver, which i've done the whole time. If I shut down the server while the site is still opened in the browser, then the changes also get applied. If I look at the requests with dev tools in the browser. I see that only the successfull requests are finishing and the unsuccessfull ones are left pending forever. Thats why the changes get applied when the server is shut down and all pending requests get closed with errors. The Server uses the Node.js "fs" module and its readFile method.
I will now try to turn the styles around so all images start off gray and without "onclick" - methods and only become unlocked once the file is found. This way the images with pending requests remain gray.
I have an Ajax script that causes the entire page to reload without ever submitting the URL for the request in the script. The server logs show the page URL as being re-submitted. Adding an alert demonstrates that the function is being run, but the embedded URL seems to be ignored. When used by itself, the request URL in the script returns the correct data.
Why isn't the embedded URL applied?
Another Ajax script on the same page works fine using a var named xhttp instead of xfiles so there's no conflict in that.
function rlist() {
var xfiles = new XMLHttpRequest();
xfiles.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
document.getElementById("filelist").innerHTML =
this.responseText;
}
};
xfiles.open("GET", "/cgi-bin/cnc.cgi?precert~patients~rlist~813527153~0975184859230735~~6306919737~622156596S", true);
xfiles.send();
}
The objective is to refresh a small table of uploaded files. The responseText contains the table html with links. That can't be the issue here though since the URL is never submitted in the first place.
Swetank Poddar actually had the right idea... As it turns out, it was user error. I had left out the colon in javascript:void(0) and continuously overlooked it. So the Ajax was running correctly but the typo in the link was causing the page to subsequently reload. It was all so fast that it wasn't obvious and the database on the server showed the last processed hit as the link to load the page in the first place, which was the link to reload it as well.
I want to develop a Chrome extension, just imagine when Facebook loads you are allowed to add extra JS on it.
But my problem is I can't modify the DOM of the later content, which means the newly loaded content that appear when the user scrolled down.
So I want to detect XHR using JavaScript.
I tried
send = XMLHttpRequest.prototype.send;
XMLHttpRequest.prototype.send = function() {
/* Wrap onreadystaechange callback */
var callback = this.onreadystatechange;
this.onreadystatechange = function() {
if (this.readyState == 4) {
/* We are in response; do something, like logging or anything you want */
alert('test');
}
callback.apply(this, arguments);
}
_send.apply(this, arguments);
}
But this is not working.. any ideas?
Besides Arun's correct remark that you should use _send for both, your approach doesn't work because of how Content Scripts work.
The code running in the content script works in an isolated environment, to prevent it from conflicting with page's own code. So it's not like you described - you're not simply adding JS to the page, you have it run isolated. As a result, your XHR replacement only affects XHR calls from your extension's content scripts and not the page.
It's possible to inject the code into the page itself. This will affect XHR's from the page, but might not work on all pages, if the Content Security Policy of the page in question disallows inline code. It seems like Facebook's CSP would allow this. Page's CSP should not be a problem according to the docs. So, this approach should work, see the question I linked.
That said, you're not specifically looking for AJAX calls, you're looking for new elements being inserted in the DOM. You can detect that without modifying the page's code, using DOM MutationObservers.
See this answer for more information.
to detect AJAX calls on a webpage you have to inject the code directly in that page and then call the .ajaxStart or .ajaxSuccess
Example:
// To Successfully Intercept AJAX calls, we had to embed the script directly in the Notifications page
var injectedCode = '(' + function() {
$('body').ajaxSuccess(function(evt, request, settings) {
if (evt.delegateTarget.baseURI == 'URL to check against if you want') {
// do your stuff
}
});
} + ')();';
// Inserting the script into the page
var script = document.createElement('script');
script.textContent = injectedCode;
(document.head || document.documentElement).appendChild(script);
script.parentNode.removeChild(script);
Greetings,
my xul app needs to load scripts dynamically, for this I derived a function that works in regular html/js apps :
function loadScript(url)
{
var e = document.createElement("script");
e.src = url;
e.type="text/javascript";
document.getElementsByTagName("head")[0].appendChild(e);
}
to something that ought work in XUL :
function loadScript( url)
{
var e = document.createElement("script");
//I can tell from statically loaded scripts that these 2 are set thru attributes
e.setAttribute( 'type' , "application/javascript" ); //type is as per MDC docs
e.setAttribute( 'src' , url );
//XUL apps attach scripts to the window I can tell from firebug, there is no head
document.getElementsByTagName("window")[0].appendChild(e);
}
The script tags get properly added, the attributes look fine,but it does not work at all, no code inside these loaded scripts is executed or even parsed.
Can any one give a hint as to what might be going on ?
T.
Okay,
as usual whenever I post on stack overflow, the answer will come pretty soon thru one last desperate Google search.
This works :
//Check this for how the url should look like :
//https://developer.mozilla.org/en/mozIJSSubScriptLoader
function loadScript( url)
{
var loader = Components.classes["#mozilla.org/moz/jssubscript-loader;1"].getService(Components.interfaces.mozIJSSubScriptLoader);
//The magic happens here
loader.loadSubScript( url );
}
This will only load local files, which is what I need for my app.
I am fairly disappointed by Mozilla, why not do this the same way like html, in a standard way ?
I've tried this, and I think you're right - I can't seem to get XUL to run dynamically appended script tags - perhaps it's a bug.
I'm curious as to why you would want to though - I can't think of any situation where one would need to do this - perhaps whatever you're trying could be achieved another way. Why is it they need to be dynamically loaded?
Off-topic: on the changes you made to the script.
e.setAttribute('src',url); is valid in normal webpages as well, and is actually technically more "correct" than e.src=url; anyway (although longer and not well supported in old browsers).
Types application/javascript or application/ecmascript are supposed to work in normal webpages and are more "correct" than text/javascript, but IE doesn't support them so they're not normally used.
Inside xul environment you are only allowed to use XHR+eval like the following:
function loadScript (url) {
var xhr = new XMLHttpRequest();
xhr.open("GET", url, false); // sync
xhr.send(null);
if (xhr.status && xhr.status != 200)
throw xhr.statusText;
try {
eval(xhr.responseText, window);
} catch (x) {
throw new Error("ERROR in loadScript: Can't load script '" + url+ "'\nError message is:" + x.message);
}
};
I can detect when the content of an iframe has loaded using the load event. Unfortunately, for my purposes, there are two problems with this:
If there is an error loading the page (404/500, etc), the load event is never fired.
If some images or other dependencies failed to load, the load event is fired as usual.
Is there some way I can reliably determine if either of the above errors occurred?
I'm writing a semi-web semi-desktop application based on Mozilla/XULRunner, so solutions that only work in Mozilla are welcome.
If you have control over the iframe page (and the pages are on the same domain name), a strategy could be as follows:
In the parent document, initialize a variable var iFrameLoaded = false;
When the iframe document is loaded, set this variable in the parent to true calling from the iframe document a parent's function (setIFrameLoaded(); for example).
check the iFrameLoaded flag using the timer object (set the timer to your preferred timeout limit) - if the flag is still false you can tell that the iframe was not regularly loaded.
I hope this helps.
This is a very late answer, but I will leave it to someone who needs it.
Task: load iframe cross-origin content, emit onLoaded on success and onError on load error.
This is the most cross browsers origin independent solution I could develop. But first of all I will briefly tell about other approaches I had and why they are bad.
1. iframe That was a little shock for me, that iframe only has onload event and it is called on load and on error, no way to know it is error or not.
2. performance.getEntriesByType('resource'). This method returns loaded resources. Sounds like what we need. But what a shame, firefox always adds Resource in resources array no matter it is loaded or failed. No way to know by Resource instance was it success. As usual. By the way, this method does not work in ios<11.
3. script I tried to load html using <script> tag. Emits onload and onerror correctly, sadly, only in Chrome.
And when I was ready to give up, my elder collegue told me about html4 tag <object>. It is like <iframe> tag except it has fallbacks when content is not loaded. That sounds like what we are need! Sadly it is not as easy as it sounds.
CODE SECTION
var obj = document.createElement('object');
// we need to specify a callback (i will mention why later)
obj.innerHTML = '<div style="height:5px"><div/>'; // fallback
obj.style.display = 'block'; // so height=5px will work
obj.style.visibility = 'hidden'; // to hide before loaded
obj.data = src;
After this we can set some attributes to <object> like we'd wanted to do with iframe. The only difference, we should use <params>, not attributes, but their names and values are identical.
for (var prop in params) {
if (params.hasOwnProperty(prop)) {
var param = document.createElement('param');
param.name = prop;
param.value = params[prop];
obj.appendChild(param);
}
}
Now, the hard part. Like many same-like elements, <object> doesn't have specs for callbacks, so each browser behaves differently.
Chrome. On error and on load emits load event.
Firefox. Emits load and error correctly.
Safari. Emits nothing....
Seems like no different from iframe, getEntriesByType, script....
But, we have native browser fallback! So, because we set fallback (innerHtml) directly, we can tell if <object> is loaded or not
function isReallyLoaded(obj) {
return obj.offsetHeight !== 5; // fallback height
}
/**
* Chrome calls always, Firefox on load
*/
obj.onload = function() {
isReallyLoaded(obj) ? onLoaded() : onError();
};
/**
* Firefox on error
*/
obj.onerror = function() {
onError();
};
But what to do with Safari? Good old setTimeout.
var interval = function() {
if (isLoaded) { // some flag
return;
}
if (hasResult(obj)) {
if (isReallyLoaded(obj)) {
onLoaded();
} else {
onError();
}
}
setTimeout(interval, 100);
};
function hasResult(obj) {
return obj.offsetHeight > 0;
}
Yeah.... not so fast. The thing is, <object> when fails has unmentioned in specs behaviour:
Trying to load (size=0)
Fails (size = any) really
Fallback (size = as in innnerHtml)
So, code needs a little enhancement
var interval = function() {
if (isLoaded) { // some flag
return;
}
if (hasResult(obj)) {
if (isReallyLoaded(obj)) {
interval.count++;
// needs less then 400ms to fallback
interval.count > 4 && onLoadedResult(obj, onLoaded);
} else {
onErrorResult(obj, onError);
}
}
setTimeout(interval, 100);
};
interval.count = 0;
setTimeout(interval, 100);
Well, and to start loading
document.body.appendChild(obj);
That is all. I tried to explain code in every detail, so it may look not so foolish.
P.S. WebDev sucks
I had this problem recently and had to resort to setting up a Javascript Polling action on the Parent Page (that contains the IFRAME tag). This JavaScript function checks the IFRAME's contents for explicit elements that should only exist in a GOOD response. This assumes of course that you don't have to deal with violating the "same origin policy."
Instead of checking for all possible errors which might be generated from the many different network resources.. I simply checked for the one constant positive Element(s) that I know should be in a good response.
After a pre-determined time and/or # of failed attempts to detect the expected Element(s), the JavaScript modifies the IFRAME's SRC attribute (to request from my Servlet) a User Friendly Error Page as opposed to displaying the typical HTTP ERROR message. The JavaScript could also just as easily modify the SRC attribute to make an entirely different request.
function checkForContents(){
var contents=document.getElementById('myiframe').contentWindow.document
if(contents){
alert('found contents of myiframe:' + contents);
if(contents.documentElement){
if(contents.documentElement.innerHTML){
alert("Found contents: " +contents.documentElement.innerHTML);
if(contents.documentElement.innerHTML.indexOf("FIND_ME") > -1){
openMediumWindow("woot.html", "mypopup");
}
}
}
}
}
I think that the pageshow event is fired for error pages. Or if you're doing this from chrome, then your check your progress listener's request to see if it's an HTTP channel in which case you can retrieve the status code.
As for page dependencies, I think you can only do this from chrome by adding a capturing onerror event listener, and even then it will only find errors in elements, not CSS backgrounds or other images.
Doesn't answer your question exactly, but my search for an answer brought me here, so I'm posting just in case anyone else had a similar query to me.
It doesn't quite use a load event, but it can detect whether a website is accessible and callable (if it is, then the iFrame, in theory, should load).
At first, I thought to do an AJAX call like everyone else, except that it didn't work for me initially, as I had used jQuery. It works perfectly if you do a XMLHttpRequest:
var url = http://url_to_test.com/
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status != 200) {
console.log("iframe failed to load");
}
};
xhttp.open("GET", url, true);
xhttp.send();
Edit:
So this method works ok, except that it has a lot of false negatives (picks up a lot of stuff that would display in an iframe) due to cross-origin malarky. The way that I got around this was to do a CURL/Web request on a server, and then check the response headers for a) if the website exists, and b) if the headers had set x-frame-options.
This isn't a problem if you run your own webserver, as you can make your own api call for it.
My implementation in node.js:
app.get('/iframetest',function(req,res){ //Call using /iframetest?url=url - needs to be stripped of http:// or https://
var url = req.query.url;
var request = require('https').request({host: url}, function(response){ //This does an https request - require('http') if you want to do a http request
var headers = response.headers;
if (typeof headers["x-frame-options"] != 'undefined') {
res.send(false); //Headers don't allow iframe
} else {
res.send(true); //Headers don't disallow iframe
}
});
request.on('error',function(e){
res.send(false); //website unavailable
});
request.end();
});
Have a id for the top most (body) element in the page that is being loaded in your iframe.
on the Load handler of your iframe, check to see if getElementById() returns a non null value.
If it is, iframe has loaded successfully. else it has failed.
in that case, put frame.src="about:blank". Make sure to remove the loadhandler before doing that.
If the iframe is loaded on the same origin as the parent page, then you can do this:
iframeEl.addEventListener('load', function() {
// NOTE: contentDocument is null if a connection error occurs or if
// X-Frame-Options is not SAMESITE (which could happen with
// 4xx or 5xx error pages if the corresponding error handlers
// do not specify SAMESITE). If error handlers do not specify
// SAMESITE, then networkErrorOccurred will incorrectly be set
// to true.
const networkErrorOccurred = !iframeEl.contentDocument;
const serverErrorOccurred = (
!networkErrorOccurred &&
!iframeEl.contentDocument.querySelector('#well-known-element')
);
if (networkErrorOccurred || serverErrorOccurred) {
let errorMessage;
if (networkErrorOccurred) {
errorMessage = 'Error: Network error';
} else if (serverErrorOccurred) {
errorMessage = 'Error: Server error';
} else {
// Assert that the above code is correct.
throw new Error('networkErrorOccurred and serverErrorOccurred are both false');
}
alert(errorMessage);
}
});