Develop Reference

window.onload doesn't work at all

I made an extension for youtube new layout, but since yesterday (they had some issues with the layout) the extension stopped working.
It seems like it does not respond to the action window.onload event as I am using like so:
window.onload = function() {
$('body').on('mouseenter', '#thumbnail', function() {
console.log('test');
});
};
For some reason every time I hover on a video thumbnail, the test is not being outputted at all. It might work once every 50 times or so.
I have jquery injected above this script as well and they are both inside the head tags. Can youtube block window.onload event or am I doing something completely wrong?

Print function only works after second click

I have this function to print a DIV.
Whenever the page is loaded and I click in a "Print" link I have, the DIV is shown to be printed without CSS.
If I close Chrome's print visualization page and click in the "Print" link again, the DIV has CSS applied.
Any ideas why?
Javascript
function printDiv(divId) {
var printDivCSSpre =
'<link href="/static/assets/vendor/sb-admin-2-1.0.7/bower_components/bootstrap/dist/css/bootstrap.min.css" rel="stylesheet">' +
'<link href="/static/assets/vendor/sb-admin-2-1.0.7/dist/css/sb-admin-2.css" rel="stylesheet">' +
'<div style="width:1000px; padding-right:20px;">';
var printDivCSSpost = '</div>';
$('body').append('<iframe id="print_frame" name="print_frame" width="0" height="0" frameborder="0" src="about:blank"></iframe>');
$("link").clone().appendTo($("#print_frame").contents().find("head"));
window.frames["print_frame"].document.body.innerHTML =
printDivCSSpre + document.getElementById(divId).innerHTML + printDivCSSpost;
window.frames["print_frame"].window.focus();
var windowInstance = window.frames["print_frame"].window;
windowInstance.print();
}
HTML
<a id="print" href="#">
<i class="fa fa-print"></i> Print
</a>
<script>
$('#print').click(function () {
printDiv('report')
})
</script>
<div id="report" class="report">
<p># Generated Table#</p>
</div>
First click:
http://imgur.com/a/Go81Y
Closing the print preview page and clicking again in print
http://imgur.com/a/SCxJF

This happens because when you call your printDiv() function, css is also written using inner HTML and in this scenario CSS is not applied during first click because you wrote CSS to the elements even when they do not exist inside DIV.
The function to work as desired has to write DIV contents first and then CSS should be applied. I would say write css after contents of DIV or load on top of your HTML page and just write DIV contents.
Hope that helps.

Every thing is right just change the sequence. In browser debugger on first click it didn't show 'print_frame' in sources section while in second click it does (I am using chrome devtool).
So load in memory frame with css attributes during onload:
var windowInstance;
$(function(){
$('body').append('<iframe id="print_frame" name="print_frame" width="0" height="0" frameborder="0" src="about:blank"></iframe>');
$("link").clone().appendTo($("#print_frame").contents().find("head"));
windowInstance = window.frames["print_frame"].window;
});
and onClick just append html
$('#print').click(function () {
var divId = 'report';
var printDivCSSpre ='<div id="printReportDiv" style="width:1000px; padding-right:20px;">';
var printDivCSSpost = '</div>';
window.frames["print_frame"].document.body.innerHTML = printDivCSSpre + document.getElementById(divId).innerHTML + printDivCSSpost;
window.frames["print_frame"].window.focus();
windowInstance.print();
});
updated jsfiddle

Try this one. The problem mainly arises because the css has not been applied to the page when the print command is initiated. setTimeout is one way to solve it as others have mentioned but it is really not possible to predict how much delay you will need. Slow internet connections will require high delays before you fire the print statement. The following code, however, only fires the print event after the css has been properly applied to the iframe.
$('#print').click(function () {
if($("#print_frame").length == 0) {
$('#report').after('<iframe id="print_frame" name="print_frame" width="0" height="0" frameborder="0" src="about:blank"></iframe>');
}
var $head = $("#print_frame").contents().find("head");
// for now for ease I will just empty head
// ideally you would want to check if this is not empty
// append css only if empty
$head.empty();
$.ajax({
url : "https://dl.dropboxusercontent.com/u/7760475/reports.css",
dataType: "text",
success : function (reports) {
// grab css and apply its content to the iframe document
$head.append('<style>'+reports+'</style>');
$.ajax({
url : "https://dl.dropboxusercontent.com/u/7760475/bootstrap.css",
dataType: "text",
success : function (bootstrap) {
// grab another css and apply its content to the iframe document
// there may be better ways to load both css files at once but this works fine too
$head.append('<style>'+bootstrap+'</style>');
// css has been applied
// clone your div and print
var $body = $("#print_frame").contents().find('body');
// empty for ease
// but later append content only if empty
$body.empty();
$("#report").clone().appendTo($body);
$('#print_frame').get(0).contentWindow.print();
}
});
}
});
});

Use inline CSS instead.
Reason: When we PRINT or save as PDF if fails to fetch external css Files, So we have to use Inline css.
edited your file please see: jsfiddle.net/ytzcwykz/18/

As other people mentioned it is hard to see your problem without seeing the working example of a problem, but just guessing from the code:
Browser is not able to load the CSS before your print() call.
Browser is not able to render the CSS before your print() call.
Keeping that in mind changing your JS function that way might do the trick
function printDiv(divId) {
$("link").clone().appendTo($("#print_frame").contents().find("head"));
window.frames["print_frame"].document.body.innerHTML =
printDivCSSpre + document.getElementById(divId).innerHTML + printDivCSSpost;
window.frames["print_frame"].window.focus();
var windowInstance = window.frames["print_frame"].window;
setTimeout(function() {
windowInstance.print();
}, 0);
}
The idea behind this function is to let browser execute it's code after we added changed the HTML/CSS code in the window - see Why is setTimeout(fn, 0) sometimes useful?
WARNING: this approach is not tested for your particular problem, and it might also not work because we escape/leave the mouse-click call-stack, calling print() method might be not possible out of user-interaction stack.
UPDATE: after looking in the posted jsfiddle - my assumption was correct, the browser needs some time to load and render the CSS, that is why calling the print() right after changing iframe contents doesn't give the desired result. There are 3.5 ways to solve that:
Use events to identify when iframe's document and window has finished loading and rendering. I tried two approaches, and failed so far, need to read docs more carefully about when document and window are behiving during the loading sequence:
we can do that from outside of iframe, i.e. listen to events of iframe element and it's children
we can do that from inside of iframe, i.e. add little javascript snippet inside which will send a message to the parent window when loading is done.
Consider forming the print result different, how about print style-sheets? I.e. add one more style sheet with print-media query to the parent doc and just call print on it?
Consider forming an iframe which is already loaded and ready to be printed, but replace just the table contents inside it.

As others mentioned, The problem here is that the CSS files used are external resources and browser takes time to download and cache it locally. Once it is cached, it would serve faster and that's why it works fine from the second click.
As Anton mentioned, setTimeout is the key here! You may probably increase the timeout seconds to make that work. I tried setting it to 500ms and that worked,
setTimeout(function(){windowInstance.print();},500);

How to manually show tab loading indicator via javascript?

I'm talking about an icon that is displayed on a tab during page loading.
Chrome:
Firefox (with TreeTab plugin):
You get the idea. I want to make it seem like the page is loading, when it's already loaded. Some event fires is javascript and then the tab looks like it's being loaded. Is there a way to do that?
One way I can think of is to replace a favicon with a spinner, but I'm not sure if it's possible to change on the fly and even if it is, it would be a hassle to make it cross-browser.

I don't think it is a good idea to do it, you'll make your users do a lot of useless requests, and this kills trees : /
IMO, it's better to do all you have in the page itself, and let the browser's UI do his own stuff.
But since I liked the challenge, here is one hacky way :
Loading an iframe will trigger this icon in both chrome and Firefox[1], so you could ,
append an iframe in the document,
set its src to some huge document,
onload of the iframe, set it again with a ? cache hack,
regularly check if the duration has elapsed so you can remove the iframe's src.
[1] It seems that Firefox does trigger the icon only if it was triggered when the document was still loading.
In code :
// how to use :
showTabLoader(25000);
// takes duration in ms as only parameter
function showTabLoader(duration) {
if (!duration) return;
var now = performance.now();
// To avoid flickering, you need some big document
// Please change this url in your script, wikimedia may not be happy with us.
var url = 'https://upload.wikimedia.org/wikipedia/commons/3/35/Viborg_Katedralskole_Symmetrical.jpg';
var iframe = document.createElement('iframe');
iframe.style.display = 'none';
document.body.appendChild(iframe);
iframe.onload = function() {
if (performance.now() - now < +duration) {
this.src = url + '?' + Math.random();
}
};
var check = function(time) {
if (time - now > +duration) {
iframe.src = '';
iframe.parentNode.removeChild(iframe);
return;
}
requestAnimationFrame(check);
}
requestAnimationFrame(check);
iframe.src = url;
}

I recently thought of the same idea. A neat option is to use a dynamic favicon instead of hacking in hidden requests, which is a really bad idea in my opinion. I found this example. It's to much code to include here and doesn't work in iframes so no way of showing it directly on Stackoverflow. Instead i describe the idea behind.
https://www.cssscript.com/favicon-loading-indicator-favloader/
The idea is simple. Replace the favicon in an interval with the loading animation icons. A favicon cannot be GIF so you have to load each image step by step with JS. When you are done, simply replace it back with the original favicon.
For me this works at least in all chrome based browsers. Firefox throw some errors in this example, but i guess it can be fixed.

Alternitive:
There is no function that shows the actual loading process of the webpage. But you can do it manually, like you said!
The event below starts to run when the page is fully loaded, even after all the images are loaded:
$(window).on('load', function() {
// do stuff
});
So what you could do is set up your html like this:
<div class="preloader">
// your loader here, animations, video, gif, anything you want
</div>
<div class="main" style="display: none;">
// the page
</div>
and your jquery like this:
$(window).on('load', function() {
setTimeout(function() {
$('.preloader').css('display', 'none');
$('.main').css('opacity', '1');
}, 5000); // <-- 5seconds
});
And there you have your manual loading function! Works perfect.
Example website: ifly50
EDIT:
added code snippet
Code snippet:
$(window).on('load', function() {
setTimeout(function() {
$('.preloader').css('display', 'none');
$('.main').css('display', 'block');
}, 3000); // <-- 3 seconds
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="preloader">loading</div>
<div class="main" style="display: none;">main</div>

jQuery scroll to bottom of div is very tempremental

I am developing an instant messaging page for my website and I consequently want the div to be scrolled to the bottom so the newest message can be seen. The page is saved as a php file and uses jQuery to do the scrolling.
The code:
$(function() {
var wtf = $('#chat');
var height = wtf[0].scrollHeight;
wtf.scrollTop(height);
});
Currently I use the following code however it is very temperamental and only works about 1 in 4 times, I have not added the webpage code as it it several hundred lines however I can if necessary. Is there a better solution which works more consistently?

Alex, I would try to load this function with
$(window).load(functiion() {
//your code here
var wtf = $('#chat');
var height = wtf[0].scrollHeight;
wtf.scrollTop(height);
}
The difference between that and document.ready is document.ready fires when the document is loaded which is before the whole page loads in some instances. It will be a slightly slower load time if you do this but your script should at least work consistently. I have faced similar troubles. Give it a try and let me know how it works for you.

Add an anchor right after the div... then when you refresh... yourpage#bottomofdiv

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.