Develop Reference

HTML Image onload triggers onerror?

I have an html image that is labeled as follow
<image src = 'image.png' onerror = "handleError(this)" onload = "handleLoad(this)">
function handleError(n){
getFirstChild(n.parentNode).style.display = '',n.style.display = 'none';
}
function handleLoad(n){
getFirstChild(n.parentNode).style.display = 'none',n.style.display = '';
}
I have a separate function getFirstChild but that doesn't have anything to do with the following problem.
Basically what is happening is in IE 11 is that the onLoad handler is getting fired and my function is setting the displays correctly, however right after the onload is fired, the onerror is also fired and overwrites what the handleLoad function has done.
Sadly this application is only supported in the IE browser but its only happening in IE11 version, in IE10 this works as expected.
I'm not sure how an onLoad can trigger, and then the onError be trigger right after when the onLoad has found the image from the src.
SECOND EDIT
As the comment below shot I'm not able to reproduce this in a jfiddle on IE11. This could be because of different things my code is trying to do at the same time, but is there any way to see why the onerror handler was trigger? I tried printing out the src of the Image item but that doesn't seem to be the issue as both onError and onLoad return the same src, and the image is clearly there.
Anyway that i can see what is causing the onError to trigger?

The window.onload event is used by programmers to kick-start their web applications.IE supports a very handy (but non-standard) attribute for the tag: defer. The presence of this attribute will instruct IE to defer the loading of a script until after the DOM has loaded. This only works for external scripts however. Another important thing to note is that this attribute cannot be set using script. That means you cannot create a script using DOM methods and set the defer attribute – it will be ignored.
Using the handy defer attribute we can create a mini-script that calls our onload handler:
<script defer src="ie_onload.js" type="text/javascript"></script>
The contents of this external script would be a single line of code to call our onload event handler:
init();
function init() {
// quit if this function has already been called
if (arguments.callee.done) return;
// flag this function so we don't do the same thing twice
arguments.callee.done = true;
// do stuff
};
as we can see there are many problems associated with using DOM event handler in IE, hence conditional compilation can be one more option for OP's problem.
IMHO you should go for this link:
http://dean.edwards.name/weblog/2005/09/busted/

Event when iframe finishes loading [duplicate]

I need to execute a callback when an IFRAME has finished loading. I have no control over the content in the IFRAME, so I can't fire the callback from there.
This IFRAME is programmaticly created, and I need to pass its data as a variable in the callback, as well as destroy the iframe.
Any ideas?
EDIT:
Here is what I have now:
function xssRequest(url, callback)
{
var iFrameObj = document.createElement('IFRAME');
iFrameObj.src = url;
document.body.appendChild(iFrameObj);
$(iFrameObj).load(function()
{
document.body.removeChild(iFrameObj);
callback(iFrameObj.innerHTML);
});
}
This callsback before the iFrame has loaded, so the callback has no data returned.

First up, going by the function name xssRequest it sounds like you're trying cross site request - which if that's right, you're not going to be able to read the contents of the iframe.
On the other hand, if the iframe's URL is on your domain you can access the body, but I've found that if I use a timeout to remove the iframe the callback works fine:
// possibly excessive use of jQuery - but I've got a live working example in production
$('#myUniqueID').load(function () {
if (typeof callback == 'function') {
callback($('body', this.contentWindow.document).html());
}
setTimeout(function () {$('#frameId').remove();}, 50);
});

I am using jQuery and surprisingly this seems to load as I just tested and loaded a heavy page and I didn't get the alert for a few seconds until I saw the iframe load:
$('#the_iframe').load(function(){
alert('loaded!');
});
So if you don't want to use jQuery take a look at their source code and see if this function behaves differently with iframe DOM elements, I will look at it myself later as I am interested and post here. Also I only tested in the latest chrome.

I have had to do this in cases where documents such as word docs and pdfs were being streamed to the iframe and found a solution that works pretty well. The key is handling the onreadystatechanged event on the iframe.
Lets say the name of your frame is "myIframe". First somewhere in your code startup (I do it inline any where after the iframe) add something like this to register the event handler:
document.getElementById('myIframe').onreadystatechange = MyIframeReadyStateChanged;
I was not able to use an onreadystatechage attribute on the iframe, I can't remember why, but the app had to work in IE 7 and Safari 3, so that may of been a factor.
Here is an example of a how to get the complete state:
function MyIframeReadyStateChanged()
{
if(document.getElementById('myIframe').readyState == 'complete')
{
// Do your complete stuff here.
}
}

The innerHTML of your iframe is blank because your iframe tag doesn't surround any content in the parent document. In order to get the content from the page referred to by the iframe's src attribute, you need to access the iframe's contentDocument property. An exception will be thrown if the src is from a different domain though. This is a security feature that prevents you from executing arbitrary JavaScript on someone else's page, which would create a cross-site scripting vulnerability. Here is some example code the illustrates what I'm talking about:
<script src="http://prototypejs.org/assets/2009/8/31/prototype.js" type="text/javascript"></script>
<h1>Parent</h1>
<script type="text/javascript">
function on_load(iframe) {
try {
// Displays the first 50 chars in the innerHTML of the
// body of the page that the iframe is showing.
// EDIT 2012-04-17: for wider support, fallback to contentWindow.document
var doc = iframe.contentDocument || iframe.contentWindow.document;
alert(doc.body.innerHTML.substring(0, 50));
} catch (e) {
// This can happen if the src of the iframe is
// on another domain
alert('exception: ' + e);
}
}
</script>
<iframe id="child" src="iframe_content.html" onload="on_load(this)"></iframe>
To further the example, try using this as the content of the iframe:
<h1>Child</h1>
Google
<p>Use the preceeding link to change the src of the iframe
to see what happens when the src domain is different from
that of the parent page</p>

I wanted to hide the waiting spinner div when the i frame content is fully loaded on IE, i tried literally every solution mentioned in Stackoverflow.Com, but with nothing worked as i wanted.
Then i had an idea, that when the i frame content is fully loaded, the $(Window ) load event might be fired. And that exactly what happened. So, i wrote this small script, and worked like magic:
$(window).load(function () {
//alert("Done window ready ");
var lblWait = document.getElementById("lblWait");
if (lblWait != null ) {
lblWait.style.visibility = "false";
document.getElementById("divWait").style.display = "none";
}
});
Hope this helps.

This function will run your callback function immediately if the iFrame is already loaded or wait until the iFrame is completely loaded.
This also addresses the following issues:
Chrome initializes every iFrame with an about:blank page which will have readyState == "complete". Later, it will replace `about:blank with the actual iframe src value. So, the initial value of readyState will not represent the readyState of your actual iFrame. Therefore, besides checking for readyState value, this function also addresses the about:blank issue.
DOMContentLoaded event doesn't work with iFrame. So it uses the load event for running the callback function if iFrame isn't already loaded. The load event is equivalent to readyState == "complete" which has been used to check whether iFrame is already loaded. So, in any scenario, the callback function will run after iFrame is fully loaded.
iFrame src can have redirects and therefore load a page different from the original src url. This function will also work in that scenario.
Pass in your callback function that you want to run when the iFrame finishes loading and the <iframe> element to this function:
function iframeReady(callback, iframeElement) {
const iframeWindow = iframeElement.contentWindow;
if ((iframeElement.src == "about:blank" || (iframeElement.src != "about:blank" && iframeWindow.location.href != "about:blank")) && iframeWindow.document.readyState == "complete") {
callback();
} else {
iframeWindow.addEventListener("load", callback);
}
}

I had a similar problem as you. What I did is that I use something called jQuery. What you then do in the javascript code is this:
$(function(){ //this is regular jQuery code. It waits for the dom to load fully the first time you open the page.
$("#myIframeId").load(function(){
callback($("#myIframeId").html());
$("#myIframeId").remove();
});
});
It seems as you delete you iFrame before you grab the html from it. Now, I do see a problem with that :p
Hope this helps :).

I have a similar code in my projects that works fine.
Adapting my code to your function, a solution could be the following:
function xssRequest(url, callback)
{
var iFrameObj = document.createElement('IFRAME');
iFrameObj.id = 'myUniqueID';
document.body.appendChild(iFrameObj);
iFrameObj.src = url;
$(iFrameObj).load(function()
{
callback(window['myUniqueID'].document.body.innerHTML);
document.body.removeChild(iFrameObj);
});
}
Maybe you have an empty innerHTML because (one or both causes):
1. you should use it against the body element
2. you have removed the iframe from the your page DOM

I think the load event is right.
What is not right is the way you use to retreive the content from iframe content dom.
What you need is the html of the page loaded in the iframe not the html of the iframe object.
What you have to do is to access the content document with iFrameObj.contentDocument.
This returns the dom of the page loaded inside the iframe, if it is on the same domain of the current page.
I would retreive the content before removing the iframe.
I've tested in firefox and opera.
Then i think you can retreive your data with $(childDom).html() or $(childDom).find('some selector') ...

I've had exactly the same problem in the past and the only way I found to fix it was to add the callback into the iframe page. Of course that only works when you have control over the iframe content.

Using onload attrbute will solve your problem.
Here is an example.
function a() {
alert("Your iframe has been loaded");
}
<iframe src="https://stackoverflow.com" onload="a()"></iframe>
Is this what you want?
Click here for more information.

What event name use in Opera's userJS to trigger a function when page finished loading and has downloaded all its assets like img,script,css etc.?

This is my code:
document.addEventListener('load', function () {
alert(document.getElementsByTagName("DIV").length);
}, false);
//'load' event above doesn't show any response, alert isn't showing
alert(document.getElementsByTagName("DIV").length);
// this alert returns 0 it looks like it is called before the page DOM has loaded
window.onload = function() {
alert(document.getElementsByTagName("DIV").length);
};
//returns 0, what the... it seems DOM hasn't loaded also
// but only on some sites, here on stackoverflow and youtube it works,
//but on google.com and many other websites (pcworld.com) shows 0
The same situation in latest stable and alpha Operas.

I suggest you simply do
window.addEventListener('load', function(){}, false)
like you would in a normal script. You could use opera.addEventListener('BeforeEvent.load', ...) but that might not fire if the page's scripts do not listen for load events in some Opera versions.
Some other background reading:
window.onload vs document.onload
addEventListener("input", callback) doesn't work in opera?

Safe way to interact with page's DOM from Overlay JS

I have a Firefox extension that detects whenever a page loads in the browser and returns its window and document. I want to attach some events (that launch functions in my addon's overlay) to elements in the page, but I don't know how to do this in a way that's safe.
Here's a code sample:
var myExt = {
onInit: function(){
var appcontent = document.getElementById("appcontent");
if(appcontent){
appcontent.addEventListener("DOMContentLoaded", this.onPageLoad, true);
}
},
onPageLoad: function(e){
var doc = e.originalTarget;
var win = doc.defaultView;
doc.getElementById("search").focus = function(){
/* ... 'Some privelliged code here' - unsafe? ... */
};
}
};
So can anyone tell me what's the safe way to add these events/interact with the page's DOM?
Thanks in advance!

I think that you want to listen to the focus event, not replace the focus() function:
doc.getElementById("search").addEventListener("focus", function(event)
{
if (!event.isTrusted)
return;
...
}, false);
Usually, there is fairly little that can go wrong here because you are not accessing the page directly - there is already a security layer (which is also why replacing the focus() method will have no effect). You can also make sure that you only act on "real" events and not events that have been generated by the webpage, you check event.isTrusted for that like in the example code. But as long as you don't unwrap objects or run code that you got from the website, you should be safe.

Javascript callback when IFRAME is finished loading?

I need to execute a callback when an IFRAME has finished loading. I have no control over the content in the IFRAME, so I can't fire the callback from there.
This IFRAME is programmaticly created, and I need to pass its data as a variable in the callback, as well as destroy the iframe.
Any ideas?
EDIT:
Here is what I have now:
function xssRequest(url, callback)
{
var iFrameObj = document.createElement('IFRAME');
iFrameObj.src = url;
document.body.appendChild(iFrameObj);
$(iFrameObj).load(function()
{
document.body.removeChild(iFrameObj);
callback(iFrameObj.innerHTML);
});
}
This callsback before the iFrame has loaded, so the callback has no data returned.

First up, going by the function name xssRequest it sounds like you're trying cross site request - which if that's right, you're not going to be able to read the contents of the iframe.
On the other hand, if the iframe's URL is on your domain you can access the body, but I've found that if I use a timeout to remove the iframe the callback works fine:
// possibly excessive use of jQuery - but I've got a live working example in production
$('#myUniqueID').load(function () {
if (typeof callback == 'function') {
callback($('body', this.contentWindow.document).html());
}
setTimeout(function () {$('#frameId').remove();}, 50);
});

I am using jQuery and surprisingly this seems to load as I just tested and loaded a heavy page and I didn't get the alert for a few seconds until I saw the iframe load:
$('#the_iframe').load(function(){
alert('loaded!');
});
So if you don't want to use jQuery take a look at their source code and see if this function behaves differently with iframe DOM elements, I will look at it myself later as I am interested and post here. Also I only tested in the latest chrome.

I have had to do this in cases where documents such as word docs and pdfs were being streamed to the iframe and found a solution that works pretty well. The key is handling the onreadystatechanged event on the iframe.
Lets say the name of your frame is "myIframe". First somewhere in your code startup (I do it inline any where after the iframe) add something like this to register the event handler:
document.getElementById('myIframe').onreadystatechange = MyIframeReadyStateChanged;
I was not able to use an onreadystatechage attribute on the iframe, I can't remember why, but the app had to work in IE 7 and Safari 3, so that may of been a factor.
Here is an example of a how to get the complete state:
function MyIframeReadyStateChanged()
{
if(document.getElementById('myIframe').readyState == 'complete')
{
// Do your complete stuff here.
}
}

The innerHTML of your iframe is blank because your iframe tag doesn't surround any content in the parent document. In order to get the content from the page referred to by the iframe's src attribute, you need to access the iframe's contentDocument property. An exception will be thrown if the src is from a different domain though. This is a security feature that prevents you from executing arbitrary JavaScript on someone else's page, which would create a cross-site scripting vulnerability. Here is some example code the illustrates what I'm talking about:
<script src="http://prototypejs.org/assets/2009/8/31/prototype.js" type="text/javascript"></script>
<h1>Parent</h1>
<script type="text/javascript">
function on_load(iframe) {
try {
// Displays the first 50 chars in the innerHTML of the
// body of the page that the iframe is showing.
// EDIT 2012-04-17: for wider support, fallback to contentWindow.document
var doc = iframe.contentDocument || iframe.contentWindow.document;
alert(doc.body.innerHTML.substring(0, 50));
} catch (e) {
// This can happen if the src of the iframe is
// on another domain
alert('exception: ' + e);
}
}
</script>
<iframe id="child" src="iframe_content.html" onload="on_load(this)"></iframe>
To further the example, try using this as the content of the iframe:
<h1>Child</h1>
Google
<p>Use the preceeding link to change the src of the iframe
to see what happens when the src domain is different from
that of the parent page</p>

I wanted to hide the waiting spinner div when the i frame content is fully loaded on IE, i tried literally every solution mentioned in Stackoverflow.Com, but with nothing worked as i wanted.
Then i had an idea, that when the i frame content is fully loaded, the $(Window ) load event might be fired. And that exactly what happened. So, i wrote this small script, and worked like magic:
$(window).load(function () {
//alert("Done window ready ");
var lblWait = document.getElementById("lblWait");
if (lblWait != null ) {
lblWait.style.visibility = "false";
document.getElementById("divWait").style.display = "none";
}
});
Hope this helps.

This function will run your callback function immediately if the iFrame is already loaded or wait until the iFrame is completely loaded.
This also addresses the following issues:
Chrome initializes every iFrame with an about:blank page which will have readyState == "complete". Later, it will replace `about:blank with the actual iframe src value. So, the initial value of readyState will not represent the readyState of your actual iFrame. Therefore, besides checking for readyState value, this function also addresses the about:blank issue.
DOMContentLoaded event doesn't work with iFrame. So it uses the load event for running the callback function if iFrame isn't already loaded. The load event is equivalent to readyState == "complete" which has been used to check whether iFrame is already loaded. So, in any scenario, the callback function will run after iFrame is fully loaded.
iFrame src can have redirects and therefore load a page different from the original src url. This function will also work in that scenario.
Pass in your callback function that you want to run when the iFrame finishes loading and the <iframe> element to this function:
function iframeReady(callback, iframeElement) {
const iframeWindow = iframeElement.contentWindow;
if ((iframeElement.src == "about:blank" || (iframeElement.src != "about:blank" && iframeWindow.location.href != "about:blank")) && iframeWindow.document.readyState == "complete") {
callback();
} else {
iframeWindow.addEventListener("load", callback);
}
}

I had a similar problem as you. What I did is that I use something called jQuery. What you then do in the javascript code is this:
$(function(){ //this is regular jQuery code. It waits for the dom to load fully the first time you open the page.
$("#myIframeId").load(function(){
callback($("#myIframeId").html());
$("#myIframeId").remove();
});
});
It seems as you delete you iFrame before you grab the html from it. Now, I do see a problem with that :p
Hope this helps :).

I have a similar code in my projects that works fine.
Adapting my code to your function, a solution could be the following:
function xssRequest(url, callback)
{
var iFrameObj = document.createElement('IFRAME');
iFrameObj.id = 'myUniqueID';
document.body.appendChild(iFrameObj);
iFrameObj.src = url;
$(iFrameObj).load(function()
{
callback(window['myUniqueID'].document.body.innerHTML);
document.body.removeChild(iFrameObj);
});
}
Maybe you have an empty innerHTML because (one or both causes):
1. you should use it against the body element
2. you have removed the iframe from the your page DOM

I think the load event is right.
What is not right is the way you use to retreive the content from iframe content dom.
What you need is the html of the page loaded in the iframe not the html of the iframe object.
What you have to do is to access the content document with iFrameObj.contentDocument.
This returns the dom of the page loaded inside the iframe, if it is on the same domain of the current page.
I would retreive the content before removing the iframe.
I've tested in firefox and opera.
Then i think you can retreive your data with $(childDom).html() or $(childDom).find('some selector') ...

I've had exactly the same problem in the past and the only way I found to fix it was to add the callback into the iframe page. Of course that only works when you have control over the iframe content.

Using onload attrbute will solve your problem.
Here is an example.
function a() {
alert("Your iframe has been loaded");
}
<iframe src="https://stackoverflow.com" onload="a()"></iframe>
Is this what you want?
Click here for more information.