JavaScript - override or prevent execution - javascript

I'm working on a client project and I have to include their header and footer, which includes some core JavaScript files. I have a couple of PNGs on the page, but their core JS file is poorly coded and doesn't check for IE 7 before attempting to replace IMG tags that contain .png files with DIVS that use the AlphaImageLoader filter. The result is that in IE 7, all my .png images are replaced with DIV tags that have a default display: block, causing a linebreak after every single png image in my pages.
What I'd like to do is override their function with a better one or somehow prevent theirs from executing, but I cannot modify the JS file itself, which both defines the function and attaches it to the window onload event. I've tried redefining the function under the same name in several places (header, just before the /body tag, in $(document).ready, etc...) but the original function always seems to execute, presumably because the original function code is what is stored with the event handler, and not merely a pointer to the function.
Any way I can fix? Is there a way to selectively remove onload event handlers?

If that's the only thing running at load, I think you could do
window.onload = null;
If there are other things running, I guess you'd have to reattach them. It's a little fragile, I suppose.

In IE7 you can use the detachEvent method:-
window.detachEvent("load", fn)
where fn is the function that was attached, however since there is jquery in this mix it may be a tall order getting hold of the actual function that was attached. Most likely the actual function attached will be anonymous.

A large IFRAME between header & footer should do the trick.

Well, depending on how it was bound, you might be able to get away with something like:
window.onload = function(){
var alert=function(a){
console.log(a);
}
window.onload();
}
Obviously, you'd want to redefine something other than alert, but that might work.

maybe if that's all it does, you can write a function to reverse it, look for all png images and strip away the div, and if you want to skip certain images you can implant an attribute to those you want to treat differently
another way is to trick the function by not having the png part of the image file name, and on load, append the .png (after their onload)
or maybe you can replace your png images with another tag, and replace onload
by the way, you can know exactly whats inside the onload, if you just alert window.onload, if there is nothing but that functionality, set window.onload = null;

Have you tried using $(window).unbind("load")?

Do you know the name of the function that replaces the PNG images? If so you might be able to override the existing function by doing something like this:
// Assuming PNG function is called pngSwap
function pngSwap() {
alert('png swap');
}
$(document).ready(function() {
if (window.pngSwap && window.pngSwap.constructor === Function) {
var oldFunc = window.pngSwap;
window.pngSwap = function() {
alert('new png swap');
}
}
pngSwap();
});

Related

How to print an iFrame with stylesheet?

I've created this code to print data from an iFrame
function (data) {
var frame = $("<iframe>", {
name: "iFrame",
class: "printFrame"
});
frame.appendTo("body");
var head = $("<head></head>");
_.each($("head link[rel=stylesheet]"), function (link) {
var csslink = $("<link/>", { rel: "stylesheet", href: $(link).prop("href") })
head.append(csslink);
;});
frame.contents().find("head")
.replaceWith(head);
frame.contents().find("body")
.append(this.html());
window.frames["iFrame"].focus();
window.frames["iFrame"].print();
}
This creates an iFrame, adds a head to where it sets all the css links that are needed for this website. Then it creates the body.
Trouble is, the styling won't get applied to the print, unless I break at line frame.contents().find("head").replaceWith(head), which means that something in that part is running asynchronously.
Question is, can I somehow get the code to wait for a short while before running that line, or is there perhaps another way to do this? Unfortunately I'm not all that familiar with iFrames, so I have no clue what it's trying to do there.
This turned out to be a real hassle. I've always been reluctant to using iframes, but since there are many resources saying that using an iframe for printing more stuff than what's on the screen, we figured we'd give it a try.
This was instead solved by putting the data inside a hidden div which then was shown before a window.print(). At the same time, all other elements on the page were given a "hidden-print" class which is a class we're already using to hide elements for prints.
This might not be as elegant for the user (The div will show briefly before the user exits the print dialogue), but it's a way more simpler code to use and manage.
I think you could / should move the last focus() and print() calls to a onload handler for the iframe, to get it to happen after styles are loaded and applied.
I've just run into the same issue and did the following:
setTimeout(() => {
window.frames["iFrame"].focus();
window.frames["iFrame"].print();
}, 500)
This appears to have sorted it for me. I hate using timeout and the length is guess work at best but as it's not system critical it's something I can run with for now.

Div is not created before javascript run

I have a question about javascript/html.
First, I have this:
var post = document.body.getElementsByClassName("post");
var x=post[i].getElementsByClassName("MyDiv")[0].innerHTML;
I get from the debugger that x is not defined, it doesn't exists.
This javascript function runs onload of the body. I am sure that I gave the right classnames in my javascript, so it should find my div.
So, I read somewhere that sometimes javascript does not find an element because it is not yet there, it is not yet created in the browser ( whatever that means).
Is it possible that my function can't find the div with that classname because of this reason?
Is there a solution?
So, I read somewhere that sometimes javascript does not find an element because it is not yet there, it is not yet created in the browser ( whatever that means).
Browsers create the DOM progressively as they get the markup. When a script element is encountered, all processing of the markup stops (except where defer and async have an effect) while the script is run. If the script attempts to access an element that hasn't been created yet (probably because its markup hasn't been processed yet) then it won't be found.
This javascript function runs onload of the body.
If that means you are using something like:
<body onload="someFn()"...>
or perhaps
<script>
window.onload = function() {
someFn();
...
}
</script>
then when the function is called, all DOM nodes are available. Some, like images, may not be fully loaded, but their elements have been created.
If it means you have the script in the body and aren't using the load event, you should move the script to the bottom of the page (e.g. just before the closing body tag) and see if that fixes the issue.
Okay, instead of calling functions with
body onload, use jQuery's ready() function, or, if you don't want to use jQuery, you can use pure javascript, but this is up to you:
// jQuery
$(document).ready(function() {
var post = document.getElementsByClassName("post"),
x = post[i].getElementsByClassName("MyDiv")[0].innerHTML;
});
// JavaScript
window.onload = function initialization() {
var post = document.getElementsByClassName("post"),
x = post[i].getElementsByClassName("MyDiv")[0].innerHTML;
}
A few side notes, I don't know what the use of innerHTML
is, and also if you're doing a for loop with i then definitely
post that code, that's kind of important.
After some discussion, my answer seems to have worked for you, but you can also place your script at the end of your body tag as #RobG has suggested.

Trying to load an API and a JS file dynamically

I am trying to load Skyscanner API dynamically but it doesn't seem to work. I tried every possible way I could think of and all it happens the content disappears.
I tried console.log which gives no results; I tried elements from chrome's developers tools and while all the content's css remains the same, still the content disappears (I thought it could be adding display:none on the html/body sort of). I tried all Google's asynch tricks, yet again blank page. I tried all js plugins for async loading with still the same results.
Skyscanner's API documentation is poor and while they offer a callback it doesn't work the way google's API's callback do.
Example: http://jsfiddle.net/7TWYC/
Example with loading API in head section: http://jsfiddle.net/s2HkR/
So how can I load the api on button click or async? Without the file being in the HEAD section. If there is a way to prevent the document.write to make the page blank or any other way. I wouldn't mind using plain js, jQuery or PHP.
EDIT:
I've set a bounty to 250 ontop of the 50 I had previously.
Orlando Leite answered a really close idea on how to make this asynch api load although some features doesn't work such as selecting dates and I am not able to set styling.
I am looking for an answer of which I will be able to use all the features so that it works as it would work if it was loading on load.
Here is the updated fiddle by Orlando: http://jsfiddle.net/cxysA/12/
-
EDIT 2 ON Gijs ANSWER:
Gijs mentioned two links onto overwriting document.write. That sounds an awesome idea but I think it is not possible to accomplish what I am trying.
I used John's Resig way to prevent document.write of which can be found here: http://ejohn.org/blog/xhtml-documentwrite-and-adsense/
When I used this method, I load the API successfuly but the snippets.js file is not loading at all.
Fiddle: http://jsfiddle.net/9HX7N/
I belive what you want is it:
function loadSkyscanner()
{
function loaded()
{
t.skyscanner.load('snippets', '1', {'nocss' : true});
var snippet = new t.skyscanner.snippets.SearchPanelControl();
snippet.setCurrency('GBP');
snippet.setDeparture('uk');
snippet.draw(document.getElementById('snippet_searchpanel'));
}
var t = document.getElementById('sky_loader').contentWindow;
var head = t.document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.onreadystatechange= function() {
if(this.readyState == 'complete') loaded();
}
script.onload= loaded;
script.src= 'http://api.skyscanner.net/api.ashx?key=PUT_HERE_YOUR_SKYSCANNER_API_KEY';
head.appendChild(script);
}
$("button").click(function(e)
{
loadSkyscanner();
});
It's load skyscanner in iframe#sky_loader, after call loaded function to create the SearchPanelControl. But in the end, snippet draws in the main document. It's really a bizarre workaround, but it works.
The only restriction is, you need a iframe. But you can hide it using display:none.
A working example
EDIT
Sorry guy, I didn't see it. Now we can see how awful is skyscanner API. It puts two divs to make the autocomplete, but not relative to the element you call to draw, but the document.
When a script is loaded in a iframe, document is the iframe document.
There is a solution, but I don't recommend, is really a workaround:
function loadSkyscanner()
{
var t;
this.skyscanner;
var iframe = $("<iframe id=\"sky_loader\" src=\"http://fiddle.jshell.net/orlleite/2TqDu/6/show/\"></iframe>");
function realWorkaround()
{
var tbody = t.document.getElementsByTagName("body")[0];
var body = document.getElementsByTagName("body")[0];
while( tbody.children.length != 0 )
{
var temp = tbody.children[0];
tbody.removeChild( temp );
body.appendChild( temp );
}
}
function snippetLoaded()
{
skyscanner = t.skyscanner;
var snippet = new skyscanner.snippets.SearchPanelControl();
snippet.setCurrency('GBP');
snippet.setDeparture('uk');
snippet.draw(document.getElementById('snippet_searchpanel'));
setTimeout( realWorkaround, 2000 );
}
var loaded = function()
{
console.log( "loaded" );
t = document.getElementById('sky_loader').contentWindow;
t.onLoadSnippets( snippetLoaded );
}
$("body").append(iframe);
iframe.load(loaded);
}
$("button").click(function(e)
{
loadSkyscanner();
});
Load a iframe with another html who loads and callback when the snippet is loaded. After loaded create the snippet where you want and after set a timeout because we can't know when the SearchPanelControl is loaded. This realWorkaround move the autocomplete divs to the main document.
You can see a work example here
The iframe loaded is this
EDIT
Fixed the bug you found and updated the link.
the for loop has gone and added a while, works better now.
while( tbody.children.length != 0 )
{
var temp = tbody.children[0];
tbody.removeChild( temp );
body.appendChild( temp );
}
For problematic cases like this, you can just overwrite document.write. Hacky as hell, but it works and you get to decide where all the content goes. See eg. this blogpost by John Resig. This ignores IE, but with a bit of work the trick works in IE as well, see eg. this blogpost.
So, I'd suggest overwriting document.write with your own function, batch up the output where necessary, and put it where you like (eg. in a div at the bottom of your <body>'). That should prevent the script from nuking your page's content.
Edit: OK, so I had/took some time to look into this script. For future reference, use something like http://jsbeautifier.org/ to investigate third-party scripts. Much easier to read that way. Fortunately, there is barely any obfuscation/minification at all, and so you have a supplement for their API documentation (which I was unable to find, by the way -- I only found 'code wizards', which I had no interest in).
Here's an almost-working example: http://jsfiddle.net/a8q2s/1/
Here's the steps I took:
override document.write. This needs to happen before you load the initial script. Your replacement function should append their string of code into the DOM. Don't call the old document.write, that'll just get you errors and won't do what you want anyway. In this case you're lucky because all the content is in a single document.write call (check the source of the initial script). If this weren't the case, you'd have to batch everything up until the HTML they'd given you was valid and/or you were sure there was nothing else coming.
load the initial script on the button click with jQuery's $.getScript or equivalent. Pass a callback function (I used a named function reference for clarity, but you can inline it if you prefer).
Tell Skyscanner to load the module.
Edit #2: Hah, they have an API (skyscanner.loadAndWait) for getting a callback once their script has loaded. Using that works:
http://jsfiddle.net/a8q2s/3/
(note: this still seems to use a timeout loop internally)
In the skyrunner.js file they are using document.write to make the page blank on load call back... So here are some consequences in your scenario..
This is making page blank when you click on button.
So, it removes everything from page even 'jQuery.js' that is why call back is not working.. i.e main function is cannot be invoked as this is written using jQuery.
And you have missed a target 'div' tag with id = map(according to the code). Actually this is the target where map loads.
Another thing i have observed is maps is not actually a div in current context, that is maps api to load.
Here you must go with the Old school approach, That is.. You should include your skyrunner.js file at the top of the head content.
So try downloading that file and include in head tag.
Thanks

load specific image before anything else

I'm a creating a loading screen for website I am making. The website loads many images, scripts, etc. The HTML and CSS part is great, but I need a way to guarantee that the "loading..." image will be loaded before anything else.
I'm using jQuery, and everything is initiated within $(function () { ... });. I imagine that the code for this would need to be called before/outside that block, and the code to remove the loading screen will be called at the very end of that block. Currently, the loading image is set as a DIV background, which is the way I prefer it. However, if it's completely necessary, I will settle for an IMG tag.
Update: (solution)
I was able to answer my own question by using a combination of Robin and Vlad's responses. Both were very good, and excellent answers, however the problem is that they were aimed to load an image before another image, rather than load an image before anything else. (CSS, JS, etc...)
Here's the dirty version of what I came up with:
var files = [new Image(), document.createElement('link'), document.createElement('script')];
files[0].setAttribute('src', 'images/loading.gif');
files[1].setAttribute('rel', 'stylesheet');
files[1].setAttribute('type', 'text/css');
files[1].setAttribute('href', 'test.css');
files[2].setAttribute('type', 'text/javascript');
files[2].setAttribute('src', 'js/jquery-1.5.1.min.js');
window.onload = function (e) {
document.getElementsByTagName('head')[0].appendChild(files[1]);
document.getElementsByTagName('head')[0].appendChild(files[2]);
}
Taking a look at the load sequence on the network tab of Chrome's developer console shows that 'loading.gif' is loaded first, then 4 dummy images, then 'test.css', and then 'jquery.1.5.1.min.js'. The CSS and JS files don't begin to load, until they've been inserted into the head tag. This is exactly what I want.
I'm predicting that I may begin to have some problems, however, when I begin to load a list of files. Chrome reports that sometimes the JS file is loaded first, but the majority of the time the CSS file is loaded first. This isn't a problem, except when I begin to add files to load, I will need to ensure that jQuery is loaded before a script file that uses jQuery.
If anyone has a solution for this, or a way to detect when the CSS/JS files are finished loading, using this method, then please comment. Though, I'm not sure that it's going to be a problem yet. I may need to ask a new question in the future about this, if I start to run into problems.
Thank you to every who has helped with this issue.
Update: (glitch fix)
I ended up running into a lot of problem with this method, because the script files were being loaded asynchronously. If I would clear the browser cache, and then load the page, it would finish loading my jquery dependent files first. Then if I refreshed the page, it would work, because jquery was loaded from cache. I solved this by setting up an array of files to load, then putting the load script into a function. Then I would step through each array item using this code:
element.onload = function() {
++i; _step();
}
element.onreadystatechange = function() {
if (("loaded" === element.readyState || "complete" === element.readyState)) { ++i; _step(); }
}
You can reuse resource prealoding browser support.
I'm not sure it works across all browsers but in my case this approach helps me to load images first. Also it allows to define concrete images so UI specific could be skipped
First define in header what resource you want to preload and define resource priority
<link rel="preload" href="link-to-image" as="image">
or
<link rel="preload" href="link-to-image">
Second line allow to increase loading priority across all object types (scripts / images / styles). First line - only through images.
Then define in body link to image as usual:
<img src="link-to-image" alt="">
Here is my working example
https://jsfiddle.net/vadimb/05scfL58/
As long as the "loading..." image is positioned before any other html elements, it should load first. This of course depends on the size of the image. You could put the loading div right after the tag and position it using 'position:absolute'.
Regarding the code to remove the loading screen, one method is to do the following.
Put all the images, scripts that need to be loaded in a hidden div (display: none)
Set up a variable that will hold the total of the images / scripts to be loaded
Set up a counter variable
Attach to each image / script the "onload" event
Everytime the "onload" event is triggered it will call a function that will increment the counter variable and check if the value of the counter equals the value of the total variable
If all resources have been loaded, fire a custom event that will show the div with the images, and hide the div with the loading screen.
The code below isn't tested so it might not work. Hope it helps
var totalImages = 0;
var loadCounter = 0;
function incrementLoadCounter() {
loadCounter++;
if(loadCounter === totalImages) {
$(document).trigger('everythingLoaded');
}
}
function hideLoadingScreen() {
$('#loadingScreen').hide();
$('#divWithImages').show();
}
$(document).ready(function(e) {
$('#loadingScreen').bind('everythingLoaded', function(e) {
hideLoadingScreen();
});
var imagesToLoad = $('img.toLoad');
totalImages = imagesToLoad.length;
$.each(imagesToLoad, function(i, item) {
$(item).load(function(e) {
incrementLoadCounter();
})
});
})
I'm not sure if it's possible to enforce.
If it is, try adding this in the head-tag:
<script type="text/javascript">
if(document.images)
(new Image()).src="http://www.image.com/example.png";
</script>
In theory that may load and cache that image before anything else.
I think if you place the IMG tag at the top of your html body it will be loaded first. If you do not want to move your div just use a copy of the image tag. Once the images is loaded it will be shown in every image tag which shows the same picture.
Or you could use spin.js as loading image. It display this "loading cycle image" via javascript.
Check it out under:
http://fgnass.github.com/spin.js/

Explicitly setting load order

I have a slight problem.
I need to show some safety information in a JS drawer that the page loads with open. The images creating the drawer are kind of hefty and as such the safety text in the drawer render prior to the background, creating a really ugly loading experiance. Is there a easy way I can say
DO NOT LOAD safetyText UNTIL safetyBG is loaded ?
We're not using any libraries (i.e. jQuery) so a JS solution would have to work as a script by itself.
If I understand you correctly, you only want to display safetyText once safetyBG has fully loaded. To achieve that, hide safetyText, then check on document.onload if safetyBG has loaded. If so, show text, if not, attach function to show text to safetyBG.onload:
function showSafetyText() {
//show text
}
window.onload = function() {
var safetyBG = document.getElementById("safetyBG"); // tweak as necessary
//have to check to see if img loaded, if you would simply assign showSafetyText
//to img.onload, it would never run if the img was fully loaded already
if (!safetyBG.complete) {
safetyBG.onload = showSafetyText;
} else {
showSafetyText();
}
}
You mentioned images (rather than a single image) in your post. If that's the case you'll want to write a function that loops through the images to check to see if they've all loaded (at which time you can load the text); then attach this function to each of the images' onload events (unless all images are loaded already in which case you can simply show the text).

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