Web-based applications are programs that are designed to be used entirely within the browser. Using apps, you can do anything (well, almost!).
These days, web apps are capable of dynamic functionality that you expect from desktop applications on your computer. If you use services like Gmail or Google Maps, you’re already using apps! Apps have the following advantages over desktop applications:
Apps install in seconds, with one click of a button. When you install a web app from the Chrome web store you get some nice new features like: unlimited offline storage, geo information, notifications etc’. So as a web developer, you might want to use this channel to make your users happy (or happier).
Apps are always up-to-date. Because apps are hosted on the web where they can be instantly updated, you can be sure you’re always using the latest version of the app that’s available.
Apps won’t crash your computer. If one app misbehaves, just close its tab in the browser. Your browser and computer won’t be affected.
Here are three lists with good (to great) web apps to make you (even more) productive.
If you have other suggestions, please let me know.
Apps For Everyday
If you want to…
On a Chromebook, you could use…
Save a file
Google Docs (which are working great in offline mode since June 2012) or Box or the Generic solution CrOS Save that will give you Dropbox and many other cloud solutions.
Read my email
Gmail or other webmail services like: yahoo, hotmail etc’.
You can also try Offline Gmail to be productive on the times you don’t have an internet connection.
A web worker is a single JavaScript file loaded and executed on a separate thread (=background and not the UI thread). Dedicated web workers are linked to their owner/creator which is the script that called and loaded them. Shared web workers allow any number of scripts to communicate with a single worker.
Btw, if you missed Part1 and/or Part2 of this series, you might want to read them first.
Shared web workers are identified in two ways: either by the URL of the script used to create it or by explicit name. In the code below we will see how it can be done.
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The conference took place on Oct, 19 2011 in the Barbican Conference Centre London. My two goals where to expose enterprise web developer to the new features that HTML5 provide today and to show them how they can leverage these features when they are building enterprises web apps. The other part was to talk with CIO/CTOs about Chrome OS and to ‘bind the dots’ on: how chrome OS harnessing business and developers with more power. Overall, it was a great event in terms of the quality of the audience. Lots of enterprise web developers from financial institution, health care and other big organizations. Some of them are still struggling with IE and the Chrome Frame was a big exciting news for them. Other points I’ve took with me:
The Chromebooks were a big hit – everyone love them! I got lots of questions and the major points where around:
Security
Total cost of ownership (70% reduction)
Battery life (8.5h)
In the future, I should bring few Chromebook and have a table in the main show so people could ‘play’ with them between sessions.
Here are some of the presentations from the event:
Simple and short code to drop a stack trace to your console and/or page.
var e = new Error('dummy');
var stack = e.stack.replace(/^[^\(]+?[\n$]/gm, '')
.replace(/^\s+at\s+/gm, '')
.replace(/^Object.\s*\(/gm, '{anonymous}()@')
.split('\n');
console.log(stack);
If you wish to read the first part of this series please go to Web Workers Part 1.
The Web Workers specification defines an API for spawning background scripts in your web application. Web Workers allow you to do things like fire up long-running scripts to handle computationally intensive tasks, but without blocking the UI or other scripts to handle user interactions. They’re going to help put and end to that nasty ‘unresponsive script’ dialog that we’ve all come to love:
or if you are (still) on windows:
you will get this common unresponsive script dialog.
Workers utilize thread-like message passing to achieve parallelism. They’re perfect for keeping your UI refresh, performant, and responsive for users.
Types of Web Workers And Some Code
It’s worth noting that the specification discusses two kinds of Web Workers:
Shared Workers – This will be covered in Part 3 of this series.
Restrictions with Local Access
Due to Google Chrome’s security restrictions, workers will not run locally (e.g. from file://) in the latest versions of the browser. Instead, they fail silently! To run your app from the file:// scheme, run Chrome with the --allow-file-access-from-files flag set. It is not recommended to run your primary browser with this flag set. It should only be used for testing purposes and not regular browsing.
(!) Debug: The other good thing to know is that you can debug works in the Chrome Developer Tools by clicking on the Scripts tab, and scrolling down in the column on the right to Workers and clicking on the debug checkbox.
Other browsers do not impose the same restriction.
Same Origin Considerations
Worker scripts must be external files with the same scheme as their calling page. Thus, you cannot load a script from a data: URL or javascript: URL, and an https: page cannot start worker scripts that begin with http: URLs.
The Code
<!DOCTYPE HTML>
<html>
<head>
<title>Web Worker: The highest prime number</title>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<meta charset=utf-8 />
</head>
<style>
#actions {
position: fixed;
top: 10px;
background: lightBlue;
padding:8px;
}
h1 {
position: relative;
bottom: 10px;
left: 280px;
}
#status {
position: relative;
font-size: 120%;
background: lightyellow;
margin:8px;
}
article {
position: relative;
color:red;
}
input {
width: 80px;
height: 35px;
font-size: 120%;
}
</style>
<body>
<script>
var myWorker;
function start() {
console.log("WebWorker: Starting");
myWorker = new Worker("highPrime2.js");
myWorker.addEventListener("message", primeHandler, false);
var maxNum = $('#upto').val();
myWorker.postMessage({'cmd': 'start', 'upto': maxNum});
}
function stop() {
if (myWorker != undefined) {
var msg = "<br/>WebWorker: Terminating " + new Date();
console.log(msg);
$('#status').append(msg);
myWorker.terminate();
myWorker = null;
}
}
function primeHandler(event) {
console.log ('got e:'+event.data);
if (is_numeric(event.data)) {
$('#result').append(event.data);
}
else {
$('#status').append(JSON.stringify(event.data) );
}
}
function is_numeric(input){
return typeof(input)=='number';
}
</script>
<h1>Web Worker: The highest prime number</h1>
<article>The prime numbers:
<output id="result"></output>
<div id="status"></div>
</article>
<div id="actions">
<input type="text" name="upto" id='upto'/>
<button onclick="start()" title="Start the work">Start</button>
<button onclick="stop()" title="Stop the work and go have a drink">Stop</button>
</div>
</body>
</html>
// And here is the worker code:
<script>
//
// A simple way to find prime numbers
//
self.addEventListener('message', function(e) {
var data = e.data;
var shouldRun = true;
switch (data.cmd) {
case 'stop':
postMessage('Worker stopped the prime calculation (Al Gore is happy now) ' +
data.msg );
shouldRun = false;
self.close(); // Terminates the worker.
break;
case 'start':
postMessage("Worker start working upto: " + data.upto + " (" + new Date()+ ")<br/>");
var numbers = isPrime(data.upto);
postMessage("Got back these numbers: "+ numbers + "<br/>");
break;
default:
postMessage('Dude, unknown cmd: ' + data.msg);
};
}, false);
// simple calculation of primes (not the most efficiate - but works)
function isPrime(number) {
var numArray = "";
var this_number,divisor,not_prime;
var this_number = 3;
while(this_number < number) {
var divisor = parseInt( this_number / 2);
var not_prime = 0;
while(divisor > 1) {
if(this_number % divisor == 0) {
not_prime = 1;
divisor = 0;
}
else {
divisor = divisor - 1;
}
}
if(not_prime == 0) {
numArray += (this_number + " ");
}
this_number = this_number + 1;
}
return numArray;
}
</script>
HTML5 features appcaching, a way to make your web sites and apps work offline, and to increase their performance as well.
I’m sure you know, browsers cache HTML, CSS, JavaScript files, images and other resources of the sites you visit, to speed up the subsequent loading of pages. However, you never know when the browser might discard cached files, and so this is not a reliable way for sites to work offline. But what if we could tell the browser what to cache? Well, with HTML5 application caches (also known as ‘appcache’) we can do just that.
An appcache manifest contain several lines in that order:
In the first line we declare “CACHE MANIFEST” (required)
Second line: “CACHE:” – which specifies the URLs of resources.
We can also optionally specify which resources should not be cached, in a section of the manifest file introduced by the string “NETWORK:”. These resources aren’t just not cached, but further, won’t be used when the user is offline, even if the browser has cached them in its own caches.
We can also optionally specify fallback resources to be used when the user is not connected, in a section of the file called “FALLBACK:”
You can add comments to the file with, simply by beginning a line with “#” – that’s an important feature to make the version readable for you as a developer. It’s also a nice way to let the browser ‘know’ that something changed in our app and it’s needed to fetch a new version of the app from the network.
Here is a simple example:
CACHE MANIFEST
#version 1.0
CACHE:
#images
/images/logo.png
/images/ido-header.png
#pages
/pages/index.html
/pages/main.html
#CSS
/style/main-style.css
#scripts
/js/main-logic.js
FALLBACK:
/ /offline.html
NETWORK:
sign-new-user.html
Creating a HTML5 cache manifest file the easy way:
manifested – cool tool to save you time and from what I’ve tried it works.
http://westciv.com/tools/manifestR/ – It is a bookmarklet, which you drag to your bookmarks bar. Then, when you visit any page, you can click the manifestR button, and it will create an HTML5 appcache manifest file for that page.
Here are few tips to get your Chromebook to run (even) faster:
First, check if you don’t have too many tabs open – after all, if you open 217 tabs it might be ‘a bit’ too much for the memory. It’s like in any other computer, the memory got its limitations.
Go to: chrome://flags/ and disable all experimental flags – just to be on the safe side. Lots of them are not taking any ‘extra’ CPU cycles, but I like to keep things as trim and simple as possible.
Make sure you remove (or at least disable) unused extensions. You can go to chrome://extensions/ in order to remove them or just right click on their buttons.
Of course, that some extensions like: LastPass and others here (on your browser) to stay. After all, there are some extensions that give certain users a lot of power that ‘worth’ the tiny bit of power they are consuming from the device.
Sometimes click on Shift-Esc to open the processes list. There you can remove/kill processes that are consuming too much CPU/memory.
If you got some other tips – please let me know with the comments here or on @greenido
A new release of Chrome 15 (on the Stable Channel) is out there for Chromebooks: Acer AC700, Samsung Series 5 and Cr-48.
The conference took place on Oct, 19 2011 in t
Ido Green 