Archive for the ‘javascript’ Category

Preloading resources

Monday, October 3rd, 2011

You might have read that when optimizing your site for speed HTTP requests are something to look at – less requests mean less waiting and usually a faster site. When doing that for CSS you’re faced with a dilemma:

  1. Put all of CSS in one file, which means less requests, but also means that the first time people land on your site, they will wait longer than needed to see the content which could mean a ruined first impression.
  2. Put CSS in per-section files, which means less loading up front but more request as people drill down into different sections of the page.

When using the first option your only focus can be on how to optimize the CSS so that it loads as fast as possible and is as small as possible. As you have less files you can easily have that file minified and gzipped even if you’re not using a deployment solution that will do that for you.

Using the second variant gives you more options – you should still optimize the files, but now you have the option of deciding when to load them to make sure that the landing page does not get hit by the added request.

Even though I started with CSS preloading can be done for any resources needed on the page – fonts, scripts, images.

When to preload?

An very obvious case is a search results page. It usually has a very distinct design that requires certain resources not needed anywhere else. But that’s not enough – you need to know when the user will these resources so you don’t go preloading everything just in case. With search it’s when they focus inside a search box – they start typing the query, while you start preloading the resources in the background.

Other obvious places to preload resources:

  • My account – when users click log-in or focus into the login form
  • Checkout – when users add stuff to their cart

Other less obvious places are landing pages when the choice a user makes turns into many sub-options, especially when products have the same resources used on the content pages.

To the code!

If you’re already using a library it probably provides AJAX methods and event methods. If not, you can search MicroJS to find one and adapt the syntax.

A simple preloader is almost as simple as helloWorld – the only thing you need to make sure is that the type of data type is set to text so that it does not get executed.

window.preload = function (src) {
	$.get(src, null, null, 'text');
} // call with preload('somefile.css');

If you want to allow the loading of multiple files at once you can detect if the passed element is an array.

window.preload = function (data) {
	var a = $.isArray(data) ? data : [data];
	$.each(a, function (i, n) {
		$.get(n, null, null, 'text');
// call with preload('somefile.css');
// or preload(['somefile.css', 'otherfile.js']);

If you prefer to call the function with many parameters you can just use arguments in the each function call.

window.preload = function () {
	$.each(arguments, function (i, n) {
		$.get(n, null, null, 'text');
// call with preload('somefile.css');
// or preload('somefile.css', 'otherfile.js');

Key element is to load the resources after the window.onload has happened – this means that any resources needed for the page to function properly have been loaded. If you do stuff sooner you might have to wait for other resources like fonts, images, videos. This means you need to know if the onload event happened – if it has, preload immediately, otherwise wait for the event to fire.

(function () {
	var win = window,
		$ = window.jQuery,
		$win = $(win);
	$win.load(function () {
		$'loaded', true);
	win.preload = function (data) {
		var a = $.isArray(data) ? data : [data],
			fn = function (i, n) {
				$.each(a, function () {
					$.get(n, null, null, 'text');
		if ($'loaded')) {
		} else {
// call with preload('somefile.css');
// or preload(['somefile.css', 'otherfile.js']);

As you can see I also did a few other things – wrapped the code into a function to isolate all the variables. I also assigned window.jQuery to a local $ to make it a bit more bulletproof.

Needless to say this script needs to be loaded during the load stage. If you intend to load it afterwards you need to make sure that you properly detect the onload event – if you don’t nothing will get preloaded as it will be waiting for that event to fire.

Taking your webapp offline

Sunday, August 21st, 2011

I’ve recently done a few things that would benefit from having an offline mode. Empowered by Appcache Facts I tried to make the newly published La Vuelta 2011 results page an offline-capable app.


The goal of this exercise is twofold:

  1. To force caching of resources that slow down the loading of your page.
  2. To actually be able to use the app when offline.


It’s as simple as writing a cache manifest. It pays to name it [something].manifest, as Apache already serves the correct header with that suffix. What you do is list all the files you want cached, add stuff you allow on the network (check Appcache Facts and Dive Into HTML5 – Offline Web Applications) and it all works. Except it doesn’t.

# version 1



AJAX stuff

If you’re using AJAX to get data from a server using jsonp/script, your framework of choice (jQuery in my case) will probably default to using a no-cache approach to loading it. This will mean that it will request the file + some suffix to prevent browser caching. This will mean that the resource will not be available if you’re actually online.

You can use navigator.onLine to switch cache on/off, but I suggest you first try requesting the no-cache resource and if it errors out, request the cached resource. The benefit is that even if you are online but the server is not, the users will still see the data / use the app.

	dataType: 'script',
	url: 'resource.js',
	cache: false,
	success: successHandler,
	error: function () {
			dataType: 'script',
			url: 'resource.js',
			cache: true,
			success: successHandler

iPad issues

Fixing the AJAX meant that it worked properly on the desktop (test with Firefox that has offline mode) and in Safari on the iPad. The trouble started when I added the app to Home Screen – data failed to load. It was the same app as in Safari and it should have worked.

After some debugging I found out that the data actually was loaded but the eval failed (I was using $.getScript). Some weird testing showed that the problem was a newline character in the data. As I really liked the newline there I added some code to the error handling that removed the newline and evaled the data, then ran success. And it worked!

	dataType: 'script',
	url: 'resource.js',
	cache: false,
	success: successHandler,
	error: function () {
			dataType: 'script',
			url: 'resource.js',
			cache: true,
			success: successHandler,
			error: function (xhr) {
				eval(xhr.textResponse.replace(/\n/g, ''));


It’s somewhat hard to debug offline stuff. I suggest using a clearly visible version indicator in the file to make sure you know which version of the file you’re looking at. Also remember that the first time you load the app after changing the file & cache manifest it is served from cache. At the same time the manifest is checked and on the iPad the files are downloaded after everything else is done (app finished loading and rendering).

It works!

After these problems were solved I used the aforementioned navigator.onLine to hide stuff that normally comes from the network but is not relevant to the offline app (banners, share links, like/+1 buttons) and you can now check the La Vuelta 2011 results page.

View Source Alliance

Friday, November 19th, 2010

Most of what I learned on the web in my early years was from “View Source”. Then came the books and the conferences.

It makes me sad to see lots of sites minifying code for performance and not releasing the full version of the code so other developers could learn from it. It’s the openness that I really like about the web.

I think there should be a “View Source Alliance” that would set rules on how to release your code in a way that visitors can benefit from the speed of minified code, while web developers can still find your full files and learn from them.

I’ll set a few simple rules here, hoping somebody with more reach picks them up:

  1. If you minify the files for them, use a simple convention name.min.ext (say jquery.min.js)
  2. When you deploy minified files, also deploy their full version at name.ext (say jquery.js)
  3. If you for some reason can’t release the full files next to the minified ones, add this to the top of the minified file: /*viewsource**/ (say /*viewsource*http://*/)

This way you will not only help others, but sometimes even stop breaking the law. Because you might be using some open source code with a licence that says you must release your code with a same/similar licence.

The Cross-Origin Request Sharing (CORS) knot

Tuesday, August 3rd, 2010

As a developer for a company that does a lot of cross-domain posting I was happy to see CORS finally happening. I’ve authored jQuery.windowName plug-in to add support for cross-domain posting in the past and this was my way out – no more hacks as browser support for CORS grows.

Yeah right.

CORS is supported on XMLHttpRequest object in Gecko and Webkit. You just request something on a different domain, and if the response has the right header with the right value you get the data. In IE you have to use a new object called XDomainRequest which is somewhat similar to XMLHttpRequest, but without readystate, onreadystate event handler and basically any header getters/setters.

Sounds ok and when I first tried it I was quite happy with how it worked. But unfortunately nothing is that simple in the land of browsers. When it fails, it’s a whole new game…

Gecko (Firefox)

Same domain request:
  • 200 response: xhr = {status: 200, statusText: ‘OK’}
  • 304 response: xhr = {status: 304, statusText: ‘Not Modified’}
Cross domain request with proper headers:
  • 200 response: xhr = {status: 200, statusText: ‘OK’}
  • 304 response: xhr = {status: 0, statusText: ‘Not Modified’}
Cross domain request without proper headers:
  • 200 response: xhr = {status: 0, statusText: ‘OK’}
  • 304 response: xhr = {status: 0, statusText: ‘Not Modified’}

Webkit (Safari, Chrome)

Same domain request:
  • 200 response: xhr = {status: 200, statusText: ‘OK’}
  • 304 response: xhr = {status: 304, statusText: ‘Not Modified’}
Cross domain request with proper headers:
  • 200 response: xhr = {status: 200, statusText: ‘OK’}
  • 304 response: xhr = {status: 304, statusText: ‘Not Modified’}
Cross domain request without proper headers:
  • 200 response: xhr = {status: 0, statusText: ”}
  • 304 response: xhr = {status: 0, statusText: ”}


Same domain requests made with XMLHttpRequest, cross domain requests made with XDomainRequest.

Same domain request:
  • 200 response: xhr = {status: 200, statusText: ‘OK’}
  • 304 response: xhr = {status: 304, statusText: ‘Not Modified’}
Cross domain request with proper headers:
  • 200 response: onload invoked
  • 304 response: onload with cache, onerror otherwise
Cross domain request without proper headers:
  • 200 response: onerror invoked
  • 304 response: onerror invoked

Where’s the knot?

The problem with this is the lack of error handling. Firefox will return status 0 on all errors, but will indicate what the response was with statusText. It will also return 0 on a 304 response, which is a bit weird. Webkit on the other hand only returns status 0 on failed requests, but without telling you what’s wrong. You get the same error when a preflight request fails, a 500 error on the server or the real request fails. IE with its own separate XDomainRequest implementation simplifies this two handlers – onload and onerror. Unfortunately it raises an onerror request when a 304 is returned on empty cache.

jQuery issues

If you’re working with jQuery (and possibly other libraries) you’re in for a treat. Opera 9.5 falsely reports status = 0 when a HTTP status 304 is returned from the server. For this reason jQuery treats status === 0 as a successful request. Thus you have no way of knowing whether your request was a success or a failure.

Untying the knot

If you intend to use jQuery’s built-in methods you’ll need to do your own bookkeeping:

  1. Know when a request is a CORS request
  2. Wait for complete event
  3. If data is empty trigger error handling

For this to work you obviously always need some data. If empty data is valid you’re screwed.

Easy way out

You might have noticed before that I made a jQuery.windowName plugin. It still has the same name, but now also supports CORS requests and does some of the CORS related bookkeeping. As the latest version is still in testing you can get it directly at (test page).

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An Event Apart Seattle review – day 1

Wednesday, June 2nd, 2010
An Event Apart Seattle
Image by Heather L via Flickr

“This is your pilot speaking. We’ve been notified that the passenger bridge has a flat tire.” were the first few words after landing in Chicago, the third airport of the day. I left Ljubljana at 7:15 CEST towards Amsterdam, switched planes and continued towards Chicago. Fortunately the issue with the gates was small enough not to endanger my connection for the last leg – to Seattle, where I landed around 16:15 PST (around 18 hours after taking off from Ljubljana).

I came to Seattle to attend An Event Apart, a conference I wanted to attend since it was first announced. Meeting people like Jeffrey Zeldman and Eric Meyer and learning from them is just amazing. But first I needed to get to the hotel in downtown Seattle and get some sleep.

After a really long day the light rail ride from the Sea-Tac airport to downtown Seattle was really amazing. Going through the suburbs, enjoying the displays of American culture – the highways, the trucks, the architecture, the people. There were only a few of us on the train at the first stop, but at the next stop loads of people got on wearing bright green shirts, scarfs and even a few kids with their faces painted green/blue – fans of Seattle Sounders FC. I thought to myself – nah, it can’t be soccer.

As I arrived a day early I had a day to spare to see the city. I woke up late and then visited The Space Needle – amazing views even in cloudy weather. I didn’t take the old-school monorail built for the world fair in 1962 thinking I’ll do that some other day. After registering at the wonderful Bell Conference Center (thanks to Marci for resolving the issues and sorry I woke you up Gašper) I walked through town to the Pike Place Market and to the high street stores – and wandered into a huge Anime convention (Sakura-Con) and a bunch of kids (not even teenagers?) wearing totally inappropriate clothes.

The day ended with a karaoke meet-up set up by Jeff Croft. I met Mike Davidson of the Newsvine fame (thanks for the beer!) and I heard Andy Clarke and Jeremy Keith sing Ace of Spades together.

The conference started on Monday with breakfast – a really good one. And then two days of talks and an additional day of workshops. I’ll review them in different depth.

Jeffrey Zeldman – Put Your Worst Foot Forward

I wanted to see Jeffrey talk for some time now. I also got to meet him just before the conference started which made me want to see this even more as he’s a really friendly guy with years of experience to share. And the talk proved to be all that and more. Explaining his mistakes from the past and the ways he is solving them – teaching what to do with anti-patterns (to quote Jeremy Keith) was really effective and I think we were all nodding as it seems we all do the same mistakes.

The checklist

  1. Know before you go.
  2. Keep expectations on track and in sync.
  3. Constantly course-correct.
  4. Tell the TRUTH.
  5. Phrase it from the client’s/boss’s point of view.
  6. Report bad news before the client/boss notices it.
  7. Have a recovery plan.
  8. Apologize-but never denigrate yourself or your team.
  9. Have an exit strategy.
  10. Know when to quit.


Working with clients is a long distance relationship – away from sight, away from heart. You need to put more energy into syncing and you need to make sure you see things with their eyes. And as in any relationship – you need to know when to leave.

Nicole Sullivan – Object Oriented CSS

Nicole used to work for Yahoo! and recently helped Facebook optimize their stylesheets, so you might say she has some experience in building and maintaining CSS systems. But unfortunately it also means that a lot of us cannot relate to some stuff she is saying. One of the first thoughts I had was that she might be a good person to write the “CSS – The Good Parts” – she even quoted Douglas Crockford in her presentation.


There were a few points that I couldn’t agree with when she said them and decided that I will think about them later. I’m not saying they’re bad practice, I just don’t think they’re good advice for most of us.

  1. Don’t use specificity was one of the things that seem like throwing away a really powerful tool because some people can’t handle the power. I could probably agree with this in big systems, but it sounds like one of the reasons to adopt Java – it’s easy for beginners to start doing productive stuff and hard for them to screw things up.
  2. Don’t use .class1.class2 as that causes all sorts of cross-browser issues. I would classify this as good stuff but it seems only IE6 is affected. So I couldn’t care less…
  3. Hacks shouldn’t change specificity as you’re not using specificity at all. That means that Modernizr and all other tools that add a class to the HTML/body elements are out of the question. The solution – using _property:value; – was something I don’t feel good about – using such invalid hacks just seems wrong.
  4. To define headers use h1, .h1 {} and in HTML use <h2 class=”h1″>…</h2> if necessary. That just seems wrong even though I agree that reusing styles is important.
  5. Avoid specifying location when targeting elements. When you do that moving an element into a different context loses the styles.

Good stuff

This list is what I think can mostly be used today for most of the people writing CSS. It is not a set of rules to abide in every case, but it should be your main modus operandi.

  1. Reuse code as much as possible. If you’re copy pasting, you’re doing it wrong. One of the ways to do this is by following the second rule.
  2. Don’t use ids, inline styles and !important to write easily applicable code. You should not write location specific code. Don’t use .sidebar ul, but rather add a class (eg. sidenav) to that ul and use .sidenav for the rule. Smaller CSS yes, but it will also get you bigger HTML (and classitis?).
  3. Think in modules and provide styles that are easily reusable by just using a class name in HTML. Only elements that are strictly bound to modules should have location specific selectors (but with .class, not #id).
  4. Put defaults into .class and use elm.class to apply specifics. Many elements can have .error – and all errors should have a similar look, whether they’re divs, lists or paragraphs.


  1. Variables are something a lot of people want. What I want is for them to be simple enough that people can’t abuse them to make CSS a programming language. The proposed syntax:
    • To set the variable: @variables hex {myblue:#006;}
    • To access the variable a {color:hex.myblue;}
  2. Prototypes are a really good way of providing defaults to a lot of elements at once and gets rid of rules that have many comma-delimited selectors. The proposed syntax:
    • Set a prototype with allowed child nodes: @prototype .box {margin:10px;children:b,.inner;}
    • Add styles to child nodes: .box .inner {position:relative;}
    • Use a prototype: .weatherBox {;}
    • Under the hood this translates to: @prototype .box, .weatherBox {…} .box .inner, .weatherBox .inner {…} .weatherBox {…}
    • Also allows checking code: .leftCol .inner {color:red;} is invalid as .inner is part of .box prototype and .leftCol does not extend it
  3. Mix-ins were skipped in the presentation as she was running out of time. You can think of them as small pieces of repeatable code that is only set in one place and used in others. Syntax:
    • Set a mixin: @mixin .clearfix {zoom:1}
    • Any selector that matches the mixin selector modifies it: .clearfix:after {content:”.”;display:block;height:0;clear:both;visibility:hidden;}
    • Include a mixin: .line {include:.clearfix;}
  4. Prototype sub-nodes were also skipped. They seem to allow calculations based on values defined in different sub-nodes of prototypes – they’re not meant to access computed style:
    • Use calculations: .box .bottom {height:5px;} .box .bl {height:10px;;}

Some of these changes will require us to write code for new and old browsers independently or to write a “compiler” that will compile code for older browsers. Is there one already written?


Building a CSS system means thinking about the selectors (and not the properties) and Nicole probably knows more than anyone else on that subject (to make you feel more comfortable, Jeremy Keith of Clearleft said they arrived to the same conclusion independently). Another, probably even more important takeaway is that you should think about flexible modules – sometimes stuff is more similar that it might seem at first. If you write CSS for a module that supports variations you’ll write less code that will apply faster and your visitors will be happy. If you want to look into an Object oriented CSS framework – check Nicole’s project OOCSS project at GitHub.

Dan Cederholm – The CSS3 Experience

Dan told us that we can and should use CSS3 now in non-critical areas such as experience, visual rewards, feedback and movement for users with the latest & greatest browsers. Not so much progressive enhancement as progressive enrichment.

Some ideas for use of CSS3:

  • Hover on items with RGBa background, a text-shadow and a border-radius with a transition (Sam Brown style).
  • Hover with opacity change. Create a single image, make it transparent normally and less transparent on hover. With a transition of course.
  • Multiple backgrounds to achieve a Silverback parallax effect.
  • Enriching form elements with a background gradient and border radius.
  • Making form buttons prettier with text-shadow, border-radius, box-shadow and a background gradient. Animate the focus styles.
  • Use scale transform with box-shadow and a transition for hover on images in gallery.
  • Rotation on hover for a single degree with a transition.


You can use CSS3 today, but know what others are missing so they don’t miss critical visual cues. Be subtle with these things or we’ll end back at using transitions to make stuff blink.

Luke Wroblewski – Mobile First!

Web products should be designed for mobile first. (Even if no mobile version is planned.)

Mobile is a big opportunity for growth, but you need to think about different things than when you’re doing web development like:

  • Multiple screen sizes and densities
  • Performance optimization
  • Touch targets, gestures, and actions
  • Location systems
  • Device capabilities

Designing for a smaller screen size will make you focus on core actions. To do that you’ll need to know your users. You should focus on iPhone, not (only) because of its popularity but also because it sets the design expectations very high. It also doesn’t allow any hidden features that hide in menus pressed by buttons – everything needs to be on the interface. When designing you should define device groups, create a default reference design and define rules for content and design adaptation – opt for web standards and a flexible layout. Technically you need to take care that you reduce requests and file size. You should take advantage of HTML5 that allows you to cache things locally and gives you the canvas tag that might sometimes be smarter than loading images. Think outside your web box – less cross browser issues means some new tricks come into play (like data URLs).

The context of using mobile applications is different. It’s not a long time sitting in front of a computer but rather quick bursts of attention everywhere, using mostly just one hand.

Mobile is innovating fast and you should think about the new capabilities to innovate yourself. Touch interfaces mean no hovers, thinking about bigger touch targets and a bunch of gestures that differ from platform to platform. Location information (from GPS, WiFi, cell towers or IP) is almost ubiquitous and can be used for positioning and filtering, but you should not forget other innovations that are less obvious like orientation information, audio & video input and output, compass, push notifications, Bluetooth connections, proximity sensors, ambient light detectors,…


You need to think about mobile because it’s an opportunity for growth, the constraints will give you the focus you need to make a great product and the capabilities will drive innovation in your product. But don’t forget that the design considerations are different.

Aarron Walter – Learning To Love Humans—Emotional Interface Design

There’s a lot of talk about usability of web pages, but is this enough? Usable is just edible. Would you say you go to the restaurant because their food is edible? We have a few options on how to trigger an emotional response to our designs – one of them is giving our sites personality. It’s a platform for emotional response as we like to empathize and personality invites empathy.

People will forgive shortcomings, follow your lead and sing your praises if you reward them with positive emotion.

You can use treats to give users something more. Let users discover new things. It’s the little positive surprises that make us happy.


Usability is not enough, we need to think about designing pleasurable experiences. We need to create an emotional response from our users and make them want to come back.

Jared Spool – Anatomy of a Design Decision

How do we make design decisions and what kind of designs exist? There are a few decision styles:

  1. Unintentional design – when users will put up with whatever we give them and we don’t care about support costs and frustration (think airlines & hotels).
  2. Self design – works great when users are like us and we are our own users (think 37signals).
  3. Genius design – when we have domain knowledge that informs our decisions and we’re solving same design problems repeatedly.
  4. Activity focused design – when we can identify users and record their activities to go beyond our previous experiences.
  5. Experience focused design – when we want to improve our users’ complete experiences, in between specific activities.

There are ways of moving up the chain:

  • “Eat your own dog food” to get from unintentional to self design.
  • Do usability testing to get from self design to genius design.
  • Field studies get you from genius design to activity focused design.
  • Personas & patterns help you get to experience focused design.

There are two fundamentally opposite ways we can make decisions:

  1. Rule-based decisions are based on design books, brand identities and other rules. They don’t allow exceptions and ignore the knowledge of the person deciding.
  2. Informed decisions are based on design patterns and put the person deciding behind the wheel. They are good for handling exceptions.

With this in mind we can look into what is needed to do one or the other:

  1. Dogma
  2. Methodologies
  3. Process
  4. Techniques
  5. Tricks

The first two are typical for rule-based decision making as they rely on a set of rules and don’t require a lot of knowledge from the person deciding. Techniques and tricks on the other hand come with experience and a lot of domain knowledge.


You need to know which decision style you’re using and encourage informed decisions, avoiding rule-based decision making. Techniques and tricks are more effective than methodologies and dogma even though/because they’re harder to come by.

Pete LePage – Help Us Kill IE6

A sponsored talk that didn’t really turn out as bad as some I’ve seen at other conferences (eg. FOWD). Pete presented the history and some IE9 features. He also suggested that we let IE6 users know that they might want to upgrade their browser as Facebook does.

MediaTemple Party

The party was nice – being fashionably late meant that it wasn’t too crowded and that most of the snacks had already gone. I had a brief chat about designing Drupal 7 with Mark Boulton, met Aarron Walter and Petra Gregorová formerly from Slovakia and a police man from Denmark that does web development in spare time. And I grabbed a (mt) beer and a coaster as a souvenir.

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Know a JavaScript developer?

Tuesday, July 21st, 2009

If you haven’t heard yet, we’re looking for a JavaScript developer at Zemanta. I think the ad says it all.

Are you the frontend developer we are looking for?

Zemanta is developing a platform for contextually enhancing content and your job would be to help us develop tools that make this easy and fun for writers and readers alike.

If you have an exceptional understanding of Javascript and the internals of browsers, thrive on challenges and love learning new skills, then we would love to talk to you. Knowing Python and Django framework is a plus, but not a prerequisite.

“I have nothing to offer but blood, toil, tears and sweat.”

(Winston Churchill on life at a startup)

Well, not quite. Working in a startup means working in an ever-changing environment. We expect you to be flexible, do what needs to be done when needed, but offer flexibility in return. We care about good work and meeting deadlines. We don’t care where or when you do it, as long as you keep true to mutual agreements which include occasional meetings and we promise not to overburden you with work. A self-reliant member of a team is how you see yourself.

Schools you might have attended are none of our concern. We care only about how good of a developer and person you are. We expect you to send us examples of your work or explain persuasively why we should hire you. Zemanta is an international company, so your application, as much of our communication, will have to be in English.

Please send your application saved as an HTML or TXT document to [email protected].

Closing date for applications: 31.7.2009

In a time when practically all pages include some sort of JavaScript I am surprised that we don’t have more JavaScript developers popping up – this now surely is a full time job even in Slovenia. So you are one challenge yourself and send your job application and if you know one, send him our way…

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