start to preload content after a complete page load

start to preload content after a complete page load - javascript

i am trying to make the preloading work in such a way that the components i wish to preload start to load after successfully loading the page.
for example,
i have index.php. i want it to load up completely.
as soon as it loads up i want to start loading the other components.
to make things clear. i have a nav that makes use of large size images. if i load them along with the index.php file, it would increase load up time of the page. i wish for those large images to load after completely rendering index.php?
am i making sense? is it possible?

Just attach your preloading function to the window object's 'load' event. Load fires after the page (and all external resources) are completely loaded.
This is different from the "DOMReady" event that various libraries like JQuery provide (as in Ivo's answer). $(document).ready(fn) will fire off once the DOM is ready (meaning the complete http document has been received/parsed) but does not wait for external resources (images, css, etc) to download.
Instead, you want $(window).load():
<script type="text/javascript">
preLoadStuff = function(){
//code that does preloading goes here
}
$(window).load(preLoadStuff);
</script>
That will trigger your preLoadStuff handler after all images, etc, are completely loaded.

The images are loaded almost in parallel to the PHP program execution. That is actually depends on the time it takes to execute your PHP program, the speed transfer of the data that you output to the browser etc.
You shouldn't try to load those images after processing index.php, that wouldn't help, because that your server is the one who process the PHP script, while the browser is the one who should fetch the images.
Having your PHP program to output the image tags as soon as possible is good and improves user experience.

I don't think you understand how a webpage works. The index.php file will execute everything it needs before any HTML output even begins processing, which takes mere milliseconds. Then HTML will begin to load everything in the order it appears on the page. The page doesn't wait for the images to finish loading before it displays anything. It will display the outline of the page as it has been loaded so far and as the images finish loading simply insert them into the correct place. It sounds to me like what you want is already the way things work.

$(document).ready(function() { YOUR CODE HERE });
http://api.jquery.com/ready/

Related

Load order of js files

I can't seem to get the preloader (Query Loader 2) to load before everything else on the page.
When I refresh the page the images in the full screen slider display block down the page, then the query loader starts.
Is there a way to start the preloader before everything else on the page?
I use stack overflow alot and normally find the answer to my question but with my limited knowledge of javascript this one has got me stumped. Things I've tried:
Putting the call to queryloader2 right at the top of the page in the header.
Putting the call to the slider scripts at the bottom of the page so they load after the preloader.
Changing the z-index of the preloader to higher than the slider.
jQuery.getScript() which loaded the scripts in order but the slider still displayed block down the page and then the preloader started.
I'm thinking its to do with the load order but if you have any ideas as to what I'm doing wrong here your help would be much appreciated.
I've put a link to my site as I didn't know which piece of code to put on here and so you can see the way the preloader and slider load the wrong way round http://stavriaphotography.com

The site is quite heavy on external scripts. Here's how loading resources in browsers work:
Images are loaded asynchronously, this means browser doesn't wait for the image to load before continuing further down the DOM, however
JavaScript is loaded synchronously and you can not load the next one before the previous is loaded.
jQuery $(document).ready() function fires only when the DOM is completly loaded.
Here's what going on, on your site:
You load jQ and queryLoader in the head and prepare to call it when DOM is ready. The scripts in the footer take time to load and are delaying the $(document).ready() function call. In the mean time you have images in your body and since they are loaded asynchronously the browser begins loading them before the queryLoader is ready to execute.
The most simple solution in your case would be to move all the external scripts to your html header, however not a very practical one.
I'd suggest reading up a bit on JavaScript and splitting up you site into multiple files for faster loading.
Some pointers: jQuery.ajax() and Handlebars.js or if you really want to go crazy dive into Backbone.js with RequireJS for asynchronous javascript loading.
Hope this helps!

Put Jquery Library first
<script src="http://code.jquery.com/jquery-1.11.0.min.js"></script>
then add your other JS files

Ajax load javascript and css with content

I am using jquery ajax to load content from one page into a div on the current one, similar to the way gmail switches between inbox, trash, etc. I am using jQuery's load method
$("#divGlobal").load("newPage.html #container");
to load the content I need into my div.
newpage.html #container also has associated javascript & css files associated with it. Right now I am loading them by appending the necessary <script> and <link> tags to <head> but it does not always work. The files always load (I am watching XHR info in Firefox) but do not always seem to work correctly.
For instance, if I load page1.html & associated files (including jQuery functions for UI), everything works fine. However, if I then load page2.html and go back to page1.html, the files load but the jQuery functions are not responding.
Is there a better way of loading javascript & css files associated with the content I am loading?

Reloading the same javascript that you have previously loaded may not do what you want because all the variables and functions are already defined from the previous load and some state may already be in place from the previous load. Loading it again into the same page doesn't start from scratch which is probably what you want.
If you control the pages you're loading, then you can write the javascript in a way that will work by just having the scripts in the content load specifically designed so that they set the state exactly how you want it and clean up any previously loaded state, but you would have to write them that way in order to work that way. This would include resetting any DOM modifications, event handlers, global variables, etc... that the first invocation of the script may have modified.

How to use Ajax to bring a page into my site then wait until it is fully loaded scripts and all

I have a site which pulls pages into a dynamic interface. Currently, the main page requires that any javascript the external pages will need be loaded with the main page. Most javascript the external pages have are objects that are built when the page gets pulled in, but first, which causes issues.
It's a little hard for me to explain for some reason so here's a simple walk through of process.
1.Request a page be pulled in
2.Based on a variable passed to function create a specific object which will be associated with the physical html coming from the page ( This is the external Javascript)
3.Load page into the objects frame
This flow requires that the external javascript be attached to the main page not the page being pulled in.
I want to switch steps 2 and 3, but I assume that I will need a way to know that the page and all its scripts have fully loaded before attempting to create the designated object, but I have no idea how to do that.
I am using jQuery and hope that this can be accomplished without a plugin but if it is needed then so be it.
Thanks
Update
Good questions. So the pages are local pages that we build at this point, so we know what to expect. Also the pages are loaded just into basic div structure.
Specifically the main page makes a request to get a page. That page is returned in the form of a string and is then pasted into a div element that is on the main page. The pages are more like fragments I guess. But they can range from fairly complicated and require a bit of javascript to not using any javascript at all.
And the external javascript would generally be added via a script tag and is not inline.
Due to the dynamic nature of the page we do NOT use IFRAME's, they cause issues with the movement of our modules.

If you're using an iframe then I imagine you are changing it's src attribute. To get an alert on when that iframe is done loading you should include a script on the page within the iframe:
<script>
$(window).load(function() {
alert("All Done");
});
</script>
If you are just requesting a string version of a page via AJAX and populating a div you need some extra JavaScript to detect when those dynamically loaded script files have finished downloading to the client.
I would visit this link to get you started.

A combination of Nick and Mic's solution.
In your IFRAME pages, you need a way to determine when the content is done loading, or ready, and then alert your main page:
<script>
$(function() {
parent.frameReady();
});
</script>
In your main page, you can code in the hook from your IFRAMEs:
<script>
function frameReady() {
// attach custom js to iframe here
}
</script>

Need help loading content via ajax

Consider the following script:
$(".workSnippet").click(function () {
//set variable portfolioCount based on index
portfolioCount = $(".workSnippet").index(this);
//load content based on portfolioCount
$('#work #cycle' + portfolioCount).load("ajax-content/ajax-content.php #portfolioImage" + portfolioCount);
// when loaded, run animation functions
$("#work").ajaxComplete(function(){
//help required here
setTimeout(invokeMultipleCycle, 200);
showWork();
});
On my page, there are multiple 'thumbnails' called .workSnippet. When you click one of these, I want it to load content via ajax. It selects what content to load in conjunction with the index function. I have this working absolutely fine.
The problem is, it's a little messy. When you click .workSnippet it runs an animation, however the high quality image loads slowly whilst the animation is taking place.
What I want to do:
Wait for the ajax request to complete before loading the functions invokeMultipleCycle and showWork.
Before the animation occurs, add an ajax loading animation absolutely positioned above .workContent.
Please bear in mind two things:
There are multiple .workSnippets on the page.
The content is not loaded in workSnippet, but another div called #work.
You will see I have already tried to attempt this uses the ajaxComplete function. However, it does not seem to work. Perhaps this is because the ajax request completes but the image still needs to 'load'?
Your help will be most appreciated.
Thanks,
Steve

Perhaps this is because the ajax
request completes but the image still
needs to 'load'?
Yes. You have to do the animation after the images load. I can't think of a way to do that off the top of my head; I think looking into something similar to document.ready() is the solution.

How can I make the browser wait to display the page until it's fully loaded?

I hate how you can actually see webpages load. I think it'd be much more appealing to wait until the page is fully loaded and ready to be displayed, including all scripts and images, and then have the browser display it. So I have two questions:
How can I do this?
Is this common practice? If not, why?

This is a very bad idea for all of the reasons given, and more. That said, here's how you do it using jQuery:
<body>
<div id="msg" style="font-size:largest;">
<!-- you can set whatever style you want on this -->
Loading, please wait...
</div>
<div id="body" style="display:none;">
<!-- everything else -->
</div>
<script type="text/javascript">
$(document).ready(function() {
$('#body').show();
$('#msg').hide();
});
</script>
</body>
If the user has JavaScript disabled, they never see the page. If the page never finishes loading, they never see the page. If the page takes too long to load, they may assume something went wrong and just go elsewhere instead of *please wait...*ing.

I think this is a really bad idea. Users like to see progress, plain and simple. Keeping the page at one state for a few seconds and then instantly displaying the loaded page will make the user feel like nothing is happening and you are likely to lose visits.
One option is to show a loading status on your page while stuff processes in the background, but this is normally reserved for when the site is actually doing processing on user input.
http://www.webdeveloper.com/forum/showthread.php?t=180958
The bottom line, you at least need to show some visual activity while the page is loading, and I think having the page load in little pieces at a time is not all that bad (assuming you aren't doing something that seriously slows down page load time).

There is certainly a valid use for this. One is to prevent people from clicking on links/causing JavaScript events to occur until all the page elements and JavaScript have loaded.
In IE, you could use page transitions which mean the page doesn't display until it's fully loaded:
<meta http-equiv="Page-Enter" content="blendTrans(Duration=.01)" />
<meta http-equiv="Page-Exit" content="blendTrans(Duration=.01)" />
Notice the short duration. It's just enough to make sure the page doesn't display until it's fully loaded.
In FireFox and other browsers, the solution I've used is to create a DIV that is the size of the page and white, then at the very end of the page put in JavaScript that hides it. Another way would be to use jQuery and hide it as well. Not as painless as the IE solution but both work well.

Here's a solution using jQuery:
<script type="text/javascript">
$('#container').css('opacity', 0);
$(window).load(function() {
$('#container').css('opacity', 1);
});
</script>
I put this script just after my </body> tag. Just replace "#container" with a selector for the DOM element(s) you want to hide. I tried several variations of this (including .hide()/.show(), and .fadeOut()/.fadeIn()), and just setting the opacity seems to have the fewest ill effects (flicker, changing page height, etc.). You can also replace css('opacity', 0) with fadeTo(100, 1) for a smoother transition. (No, fadeIn() won't work, at least not under jQuery 1.3.2.)
Now the caveats: I implemented the above because I'm using TypeKit and there's an annoying flicker when you refresh the page and the fonts take a few hundred milliseconds to load. So I don't want any text to appear on the screen until TypeKit has loaded. But obviously you're in big trouble if you use the code above and something on your page fails to load. There are two obvious ways that it could be improved:
A maximum time limit (say, 1 second) after which everything appears whether the page is loaded or not
Some kind of loading indicator (say, something from http://www.ajaxload.info/)
I won't bother implementing the loading indicator here, but the time limit is easy. Just add this to the script above:
$(document).ready(function() {
setTimeout('$("#container").css("opacity", 1)', 1000);
});
So now, worst-case scenario, your page will take an extra second to appear.

Immediately following your <body> tag add something like this...
<style> body {opacity:0;}</style>
And for the very first thing in your <head> add something like...
<script>
window.onload = function() {setTimeout(function(){document.body.style.opacity="100";},500);};
</script>
As far as this being good practice or bad depends on your visitors, and the time the wait takes.
The question that is stil left open and I am not seeing any answers here is how to be sure the page has stabilized. For example if you are loading fonts the page may reflow a bit until all the fonts are loaded and displayed. I would like to know if there is an event that tells me the page is done rendering.

Also make sure the server buffers the page and does not immediately (while building) stream it to the client browser.
Since you have not specified your technology stack:
PHP: look into ob_start
ASP.NET: make sure Response.BufferOutput = True (it is by default)

obligatory: "use jQuery"
I've seen pages that put a black or white div that covers everything on top of the page, then remove it on the document.load event. Or you could use .ready in jQuery That being said, it was one of the most anoying web pages I've ever seen, I would advise against it.

in PHP-Fusion Open Source CMS, http://www.php-fusion.co.uk, we do it this way at core -
<?php
ob_start();
// Your PHP codes here
?>
YOUR HTML HERE
<?php
$html_output = ob_get_contents();
ob_end_clean();
echo $html_output;
?>
You won't be able to see anything loading one by one. The only loader will be your browser tab spinner, and it just displays everything in an instant after everything is loaded. Give it a try.
This method is fully compliant in html files.

You can hide everything using some css:
#some_div
{
display: none;
}
and then in javascript assign a function to document.onload to remove that div.
jQuery makes things like this very easy.

In addition to Trevor Burnham's answer if you want to deal with disabled javascript and defer css loading
HTML5
<html class="no-js">
<head>...</head>
<body>
<header>...</header>
<main>...</main>
<footer>...</footer>
</body>
</html>
CSS
//at the beginning of the page
.js main, .js footer{
opacity:0;
}
JAVASCRIPT
//at the beginning of the page before loading jquery
var h = document.querySelector("html");
h.className += ' ' + 'js';
h.className = h.className.replace(
new RegExp('( |^)' + 'no-js' + '( |$)', 'g'), ' ').trim();
JQUERY
//somewhere at the end of the page after loading jquery
$(window).load(function() {
$('main').css('opacity',1);
$('footer').css('opacity',1);
});
RESOURCES
CSS delivery optimization: How to defer css loading?
What is the purpose of the HTML "no-js" class?
How to get the <html> tag HTML with JavaScript / jQuery?
How to add/remove a class in JavaScript?

While I agree with the others that you should not want it I'll just briefly explain what you can do to make a small difference without going all the way and actually blocking content that is already there -- maybe this will be enough to keep both you and your visitors happy.
The browser starts loading a page and will process externally located css and js later, especially if the place the css/js is linked is at the 'correct' place. (I think the advice is to load js as late as possible, and to use external css that you load in the header). Now if you have some portion of your css and/or js that you would like to be applied as soon as possible simply include that in the page itself. This will be against the advice of performance tools like YSlow but it probably will increase the change of your page showing up like you want it to be shown. Use this only when really needed!

You could start by having your site's main index page contain only a message saying "Loading". From here you could use ajax to fetch the contents of your next page and embed it into the current one, on completion removing the "Loading" message.
You might be able to get away with just including a loading message container at the top of your page which is 100% width/height and then removing the said div on load complete.
The latter may not work perfectly in both situations and will depends on how the browser renders content.
I'm not entirely sure if its a good idea. For simple static sites I would say not. However, I have seen a lot of heavy javascript sites lately from design companies that use complex animation and are one page. These sites use a loading message to wait for all scripts/html/css to be loaded so that the page functions as expected.

Don't use display:none. If you do, you will see images resize/reposition when you do the show(). Use visibility:hidden instead and it will lay everything out correctly, but it just won't be visible until you tell it to.

Hope this code will help
<html>
<head>
<style type="text/css">
.js #flash {display: none;}
</style>
<script type="text/javascript">
document.documentElement.className = 'js';
</script>
</head>
<body>
<!-- the rest of your code goes here -->
<script type="text/javascript" src="/scripts/jquery.js"></script>
<script type="text/javascript">
// Stuff to do as soon as the body finishes loading.
// No need for $(document).ready() here.
</script>
</body>
</html>

Put text at the top of the page. While the user reads it, the rest of the page can load and it will be ready by the time the user scrolls down.

I am, frankly, a bit disturbed at many of the answers here. I'd say all of them are terrible. Although I share the skeptical reaction of the various top respondents, many answers give "solutions" that won't display anything at all to a user who has JavaScript disabled, and many others rely on a customized on-page loading notice, while signaling to the browser that the page is already loaded.
As a user, I hate both of these outcomes, so as a web-developer, I'd say these are both "non-solutions". You never want to anger your userbase and the solutions given here will anger a lot of users. I especially hate these approaches because if the user opens a webpage in the background in a new tab, the browser will display the page as loaded but the user might click over to it to find that it isn't loaded.
Independently of your question here, best practice is to make as much of your site work without JavaScript as possible, and best practice is to use the browser's built-in loading signals and never signal to the browser that the page is loaded before it actually is. So really, the only good way to do this is to make your page load so fast that there is never any moment of the user waiting.
The best way to achieve what you want is avoid use of Javascript to load elements of the page, and then optimize the page intensely. Here are the components of this approach:
Have JavaScript on the page if you like, but don't use it to load or otherwise modify any DOM elements after the initial request is fulfilled by the server. Use JavaScript to modify elements of the page only later, such as if triggered by user input, or perhaps to refresh an element after some time, but not in any way related to the page's initial loading. I.e. use JavaScript for what it was designed for (to make webpages interactive) and don't use it to do what HTML was designed for (to make the webpage in the first place.)
Avoid the use of any heavy JavaScript libraries and include as little JavaScript as possible. Never include JavaScript files generically, i.e. only include specific files / libraries in specific pages where you need them.
Specify the width and height of any images in the page code itself, so that the browser can know the exact layout before the image loaded. This reduces any "choppiness" as the page loads, i.e. elements moving around as the browser resizes the boxes in which images of unspecified width are contained.
Ensure that image files are in the exact dimensions being displayed on the page and are not being downsized by the browser. This minimizes file size and also minimizes CPU work the user's computer needs to do to resize images, both of which can affect load time.
Optimize the compression of images, which includes using a good lossy format like JPG and lowering the compression level to as low as you can go without affecting perception. Use lossless formats like PNG only where necessary and ideally keep them small in dimension so the filesize is also small.
Focus the intensity of your optimization efforts on any elements that load "above the fold" on a typical page, as these are what is going to affect what the user sees. Users rarely scroll down instantly, so if elements lower down on the page load a bit slower, almost no one will notice. But still optimize these lower elements reasonably because they also affect server load, bandwidth, and user CPU load.
If you use any elements at all in your page that are potentially very slow to load due to reasons beyond your control, such as content pulled from another server (ads, social media widgets, integrations with other websites, etc.), compartmentalize these in an element of fixed size, and ideally place it below the fold.
Avoid auto-ads, page-modifying AI (like Ezoic), or any other external add-ins that necessarily breaks or undermines one or more of these recommendations. For example, auto-ads are terrible because they rely on loading an external resource,they usually have heavy javascript libraries, and they also modify the page layout. Even the best-designed auto-ads are going to completely undermine all your other optimization efforts.
If you are running a company with multiple developers, quickly jettison any developers who are not fully committed to a lightweight, fast-loading web design. Ideally, don't ever hire such people to begin with. A lot of people get really vested in a certain philosophy or style of development that is at odds with lightweight design. The world would be a better place if these people were in a different line of work, rather than designing webpages.
So you've optimized your page.
This produces the outcome that, if the user clicks the link directly, they'll see the content above the fold fully loaded immediately or nearly-immediately, worst-case-scenario being that a couple images fill in in a second or two. By the time they scroll down, everything else will already be loaded. Any truly-slow-to-load content, such as Google Analytics tracking or other third-party services, will not be central to the appearance of the webpage itself, so the user will see a fully-loaded page even if there are still a few invisible elements loading behind the scenes.
On the other hand, if the user loads the link in a background tab, it will display as loading to the browser, showing the animated symbol in the tab, until it is truly fully loaded. Once it displays as loaded in the tab, if they click it, it will be fully loaded.
In addition, you will have made the page load really fast, which is a good thing in and of itself.
This is a win-win. The user sees a full-loaded page nearly instantly, there is almost never any waiting while looking at a half-displayed page, the loading symbol works as expected when loading a tab in the background, and on top of this you've netted a ton of side-benefits like reduced bandwidth and server CPU load, not to mention lessening the load on the user's CPU as well. (Many users HATE when your page cranks their CPU, and rightfully so.)
So yeah, your choice what to do, but there is only one real solution here and it is lightweight, efficient web design.

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