Wednesday, November 7, 2012

Asynchronous JS loading without blocking onload

Asynchronous JS is best way to load js file in your HTML page but it still blocks window.onload event (except in IE before version 10).

checkout here how onload blocked even we use asyn js loading techniques

So here is another solution for same :-)
  1. create an iframe without setting src to a new URL. This fires onload of the iframe immediately and the whole thing is completely out of the way
  1. style the iframe to make it invisible
  1. get the last script tag so far, which is the snippet itself. This is in order to glue the iframe to the snippet that includes it.
  1. insert the iframe into the page
  1. get a handle to the document object of the iframe
  1. write some HTML into that iframe document
  1. this HTML includes the desired script

var iframe = document.createElement('iframe');
(iframe.frameElement || iframe).style.cssText = "width: 0; height: 0; border: 0";
var where = document.getElementsByTagName('script');
where = where[where.length - 1];
where.parentNode.insertBefore(iframe, where);
var doc = iframe.contentWindow.document;'<body onload="'+
'var js = document.createElement(\'script\');'+
'js.src = \''+ url +'\';'+


1. Avoid SSL warnings: iframe.src defaults to “about:blank” in IE6, which it then treats as insecure content on HTTPS pages. We found that initializing iframe.src to “javascript:false”.

2. Avoid crossdomain exceptions: anonymous iframe access will throw exceptions if the host page changed the document.domain value in IE. The original Meebo code falls back to a “javascript:” URL when this happens.

3. The script (asyncjs1.php) runs is in an iframe, so all document and window references point to the iframe, not the host page.There's an easy solution for that without changing the whole script. Just wrap it in an immediate function and pass the document object the script expects:

document.getElementById('r')... // all fine

4. The script works fine in Opera, but blocks onload. Opera is weird here. Even regular async scripts block DOMContentLoaded which is a shame.

seems below code solves our problem ..  try it and let me know the results ...

Tuesday, November 6, 2012

PHP's register_shutdown_function

PHP has approx. 5800 functions defined in global space .. Uff .. that is one cause that people does not consider it as thoughtful language but these APIs work as strong enough tool to accomplish various task and it provide tremendous functionality to end user.

Today we will discuss one magical function named "register_shutdown_function".

function allows you to execute a block of code whenever your script ends for any reason.
Whether your page exit()s or die()s or just finishes, a developer has a hook to run whatever code he/she deems necessary. And not just one function either… you can use this call to register as many shutdown functions as you want, and they will get executed in the order that they get applied. But of course, you must be careful: PHP will happily give you more rope than you will ever need to hang yourself. A lot of people may consider the use of this function to be magic, and you’ll want to be very clear that what you’re doing is documented.

Use of this function is very straight-forward.

I just tested with Apache, PHP being used as Apache module. I created an endless loop like this:

class X
    function __destruct()
        $fp = fopen("/var/www/dtor.txt", "w+");
        fputs($fp, "Destroyed\n");

$obj = new X();
while (true) {
    // do nothing

Here's what I found out:-

  1. pressing STOP button in Firefox does not stop this script
  2. If I shut down Apache, destructor does not get called
  3. It stops when it reaches PHP max_execution_time and destuctor does not get called

However, doing this:

function shutdown_func() {
    $fp = fopen("/var/www/htdocs/dtor.txt", "w+");
    fputs($fp, "Destroyed2\n");


while (true) {
    // do nothing

shutdown_func gets called. So this means that class destuctor is not that good as shutdown functions. :-)

Enjoy !! :-)

Tuesday, October 30, 2012

Things web developers must know

The idea here is that most of us should already know most of what is on this list. But there just might be one or two items you haven't really looked into before, don't fully understand, or maybe never even heard of.
Interface and User Experience
  • Be aware that browsers implement standards inconsistently and make sure your site works reasonably well across all major browsers. At a minimum test against a recent Gecko engine (Firefox), a WebKit engine (SafariChrome, and some mobile browsers), your supported IE browsers (take advantage of the Application Compatibility VPC Images), and Opera. Also consider how browsers render your site in different operating systems.
  • Consider how people might use the site other than from the major browsers: cell phones, screen readers and search engines, for example. — Some accessibility info: WAI and Section508, Mobile development: MobiForge.
  • Staging: How to deploy updates without affecting your users. Ed Lucas's answer has some comments on this.
  • Don't display unfriendly errors directly to the user.
  • Don't put users' email addresses in plain text as they will get spammed to death.
  • Add the attribute rel="nofollow" to user-generated links to avoid spam.
  • Build well-considered limits into your site - This also belongs under Security.
  • Learn how to do progressive enhancement.
  • Redirect after a POST if that POST was successful, to prevent a refresh from submitting again.
  • Don't forget to take accessibility into account. It's always a good idea and in certain circumstances it's a legal requirementWAI-ARIA and WCAG 2 are good resources in this area.
  • Implement caching if necessary, understand and use HTTP caching properly as well as HTML5 Manifest.
  • Optimize images - don't use a 20 KB image for a repeating background.
  • Learn how to gzip/deflate content (deflate is better).
  • Combine/concatenate multiple stylesheets or multiple script files to reduce number of browser connections and improve gzip ability to compress duplications between files.
  • Take a look at the Yahoo Exceptional Performance site, lots of great guidelines including improving front-end performance and their YSlow tool. Google page speed is another tool for performance profiling. Both require Firebug to be installed.
  • Use CSS Image Sprites for small related images like toolbars (see the "minimize HTTP requests" point)
  • Busy web sites should consider splitting components across domains. Specifically...
  • Static content (i.e. images, CSS, JavaScript, and generally content that doesn't need access to cookies) should go in a separate domain that does not use cookies, because all cookies for a domain and its subdomains are sent with every request to the domain and its subdomains. One good option here is to use a Content Delivery Network (CDN).
  • Minimize the total number of HTTP requests required for a browser to render the page.
  • Utilize Google Closure Compiler for JavaScript and other minification tools.
  • Make sure there’s a favicon.ico file in the root of the site, i.e. /favicon.icoBrowsers will automatically request it, even if the icon isn’t mentioned in the HTML at all. If you don’t have a/favicon.ico, this will result in a lot of 404s, draining your server’s bandwidth.
SEO (Search Engine Optimization)
  • Use "search engine friendly" URLs, i.e. use instead
  • When using # for dynamic content change the # to #! and then on the server$_REQUEST["_escaped_fragment_"] is what googlebot uses instead of #!. In other words,./#!page=1 becomes ./?_escaped_fragments_=page=1. Also, for users that may be using FF.b4 or Chromium, history.pushState({"foo":"bar"}, "About", "./?page=1"); Is a great command. So even though the address bar has changed the page does not reload. This allows you to use ? instead of #! to keep dynamic content and also tell the server when you email the link that we are after this page, and the AJAX does not need to make another extra request.
  • Don't use links that say "click here". You're wasting an SEO opportunity and it makes things harder for people with screen readers.
  • Have an XML sitemap, preferably in the default location /sitemap.xml.
  • Use  when you have multiple URLs that point to the same content, this issue can also be addressed from Google Webmaster Tools.
  • Use Google Webmaster Tools and Bing Webmaster Tools.
  • Install Google Analytics right at the start (or an open source analysis tool like Piwik).
  • Know how robots.txt and search engine spiders work.
  • Redirect requests (using 301 Moved Permanently) asking for to the other way round) to prevent splitting the google ranking between both sites.
  • Know that there can be badly-behaved spiders out there.
  • If you have non-text content look into Google's sitemap extensions for video etc. There is some good information about this in Tim Farley's answer.
  • Understand HTTP and things like GET, POST, sessions, cookies, and what it means to be "stateless".
  • Write your XHTML/HTML and CSS according to the W3C specifications and make sure theyvalidate. The goal here is to avoid browser quirks modes and as a bonus make it much easier to work with non-standard browsers like screen readers and mobile devices.
  • Understand how JavaScript is processed in the browser.
  • Understand how JavaScript, style sheets, and other resources used by your page are loaded and consider their impact on perceived performance. It may be appropriate in some cases to move scripts to the bottom of your pages.
  • Understand how the JavaScript sandbox works, especially if you intend to use iframes.
  • Be aware that JavaScript can and will be disabled, and that AJAX is therefore an extension, not a baseline. Even if most normal users leave it on now, remember that NoScript is becoming more popular, mobile devices may not work as expected, and Google won't run most of your JavaScript when indexing the site.
  • Learn the difference between 301 and 302 redirects (this is also an SEO issue).
  • Learn as much as you possibly can about your deployment platform.
  • Consider using a Reset Style Sheet.
  • Consider JavaScript frameworks (such as jQueryMooToolsPrototypeDojo or YUI 3), which will hide a lot of the browser differences when using JavaScript for DOM manipulation.
  • Taking perceived performance and JS frameworks together, consider using a service such as theGoogle Libraries API to load frameworks so that a browser can use a copy of the framework it has already cached rather than downloading a duplicate copy from your site.
  • Don't reinvent the wheel. Before doing ANYTHING search for a component or example on how to do it. There is a 99% chance that someone has done it and released an OSS version of the code.
Bug fixing
  • Understand you'll spend 20% of your time coding and 80% of it maintaining, so code accordingly.
  • Set up a good error reporting solution.
  • Have a system for people to contact you with suggestions and criticisms.
  • Document how the application works for future support staff and people performing maintenance.
  • Make frequent backups! (And make sure those backups are functional) Ed Lucas's answer has some advice. Have a restore strategy, not just a backup strategy.
  • Use a version control system to store your files, such as SubversionMecurial or Git.
  • Don't forget to do your Acceptance Testing. Frameworks like Selenium can help.
  • Make sure you have sufficient logging in place using frameworks such as log4jlog4net or log4r. If something goes wrong on your live site, you'll need a way of finding out what.
  • When logging make sure you're capture both handled exceptions, and unhandled exceptions. Report/analyse the log output, as it'll show you where the key issues are in your site.
Lots of stuff omitted not necessarily because they're not useful answers, but because they're either too detailed, out of scope, or go a bit too far for someone looking to get an overview of the things they should know. If you're one of those people you can read the rest of the answers to get more detailed information about the things mentioned in this list. If I get the time I'll add links to the various answers that contain the things mentioned in this list if the answers go into detail about these things. Please feel free to edit this as well, I probably missed some stuff or made some mistakes.

original source: