HTML5 Web Storage

Storing Data on the Client

HTML5 offers two new objects for storing data on the client:

• localStorage - stores data with no time limit
• sessionStorage - stores data for one session

Earlier, this was done with cookies. Cookies are not suitable for large amounts of data, because they are passed on by EVERY request to the server, making it very slow and in-effective.
In HTML5, the data is NOT passed on by every server request, but used ONLY when asked for. It is possible to store large amounts of data without affecting the website's performance.
The data is stored in different areas for different websites, and a website can only access data stored by itself.
HTML5 uses JavaScript to store and access the data.

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The localStorage Object

The localStorage object stores the data with no time limit. The data will be available the next day, week, or year.
How to create and access a localStorage:

Example

<script type="text/javascript">
localStorage.lastname="Smith";
document.write(localStorage.lastname);
</script>

Try it yourself »

The following example counts the number of times a user has visited a page:

Example

<script type="text/javascript">
if (localStorage.pagecount)
  {
  localStorage.pagecount=Number(localStorage.pagecount) +1;
  }
else
  {
  localStorage.pagecount=1;
  }
document.write("Visits "+ localStorage.pagecount + " time(s).");
</script>

Try it yourself »

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The sessionStorage Object

The sessionStorage object stores the data for one session. The data is deleted when the user closes the browser window.
How to create and access a sessionStorage:

Example

<script type="text/javascript">
sessionStorage.lastname="Smith";
document.write(sessionStorage.lastname);
</script>

Try it yourself »

The following example counts the number of times a user has visited a page, in the current session:

Example

<script type="text/javascript">
if (sessionStorage.pagecount)
  {
  sessionStorage.pagecount=Number(sessionStorage.pagecount) +1;
  }
else
  {
  sessionStorage.pagecount=1;
  }
document.write("Visits "+sessionStorage.pagecount+" time(s) this session.");
</script>

Try it yourself »

HTML5 Geolocation

HTML5 Geolocation is used to locate a user's position

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Locate the User's Position

The HTML5 Geolocation API is used to get the geographical position of a user.
Since this can compromise user privacy, the position is not available unless the user approves it.

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Browser Support

Internet Explorer 9, Firefox, Chrome, Safari and Opera support Geolocation.
Note: Geolocation is much more accurate for devices with GPS, like iPhone.

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Using Geolocation

Use the getCurrentPosition() method to get the user's position.
The example below is a simple Geolocation example returning the latitude and longitude of the user's position:

Example

<script>
var x=document.getElementById("demo");
function getLocation()
  {
  if (navigator.geolocation)
    {
    navigator.geolocation.getCurrentPosition(showPosition);
    }
  else{x.innerHTML="Geolocation is not supported by this browser.";}
  }
function showPosition(position)
  {
  x.innerHTML="Latitude: " + position.coords.latitude +
  "<br />Longitude: " + position.coords.longitude;
  }
</script>

Try it yourself »

Example explained:

• Check if Geolocation is supported
• If supported, run the getCurrentPosition() method. If not, display a message to the user
• If the getCurrentPosition() method is successful, it returns a coordinates object to the function specified in the parameter ( showPosition )
• The showPosition() function gets the displays the Latitude and Longitude

The example above is a very basic Geolocation script, with no error handling.

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Handling Errors and Rejections

The second parameter of the getCurrentPosition() method is used to handle errors. It specifies a function to run if it fails to get the user's location:

Example

function showError(error)
  {
  switch(error.code)
    {
    case error.PERMISSION_DENIED:
      x.innerHTML="User denied the request for Geolocation."
      break;
    case error.POSITION_UNAVAILABLE:
      x.innerHTML="Location information is unavailable."
      break;
    case error.TIMEOUT:
      x.innerHTML="The request to get user location timed out."
      break;
    case error.UNKNOWN_ERROR:
      x.innerHTML="An unknown error occurred."
      break;
    }
  }

Try it yourself »

Error Codes:

• Permission denied - The user did not allow Geolocation
• Position unavailable - It is not possible to get the current location
•  Timeout - The operation timed out

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Displaying the Result in a Map

To display the result in a map, you need access to a map service that can use latitude and longitude, like Google Maps:

Example

function showPosition(position)
{
var latlon=position.coords.latitude+","+position.coords.longitude;

var img_url="http://maps.googleapis.com/maps/api/staticmap?center="
+latlon+"&zoom=14&size=400x300&sensor=false";

document.getElementById("mapholder").innerHTML="<img src='"+img_url+"' />";
}

Try it yourself »

In the example above we use the returned latitude and longitude data to show the location in a Google map (using a static image).
Google Map Script
How to use a script to show an interactive map with a marker, zoom and drag options.

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Location-specific Information

This page demonstrated how to show a user's position on a map. However, Geolocation is also very useful for location-specific information.
Examples:

• Up-to-date local information
• Showing Points-of-interest near the user
• Turn-by-turn navigation (GPS)

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The getCurrentPosition() Method - Return Data

The getCurrentPosition() method returns an object if it is successful. The latitude, longitude and accuracy properties are always returned. The other properties below are returned if available.

Property	Description
coords.latitude	The latitude as a decimal number
coords.longitude	The longitude as a decimal number
coords.accuracy	The accuracy of position
coords.altitude	The altitude in meters above the mean sea level
coords.altitudeAccuracy	The altitude accuracy of position
coords.heading	The heading as degrees clockwise from North
coords.speed	The speed in meters per second
timestamp	The date/time of the response

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Geolocation object - Other interesting Methods

watchPosition() - Returns the current position of the user and continues to return updated position as the user moves (like the GPS in a car).
clearWatch() - Stops the watchPosition() method.
The example below shows the watchPosition() method. You need an accurate GPS device to test this (like iPhone):

Example

<script>
var x=document.getElementById("demo");
function getLocation()
  {
  if (navigator.geolocation)
    {
    navigator.geolocation.watchPosition(showPosition);
    }
  else{x.innerHTML="Geolocation is not supported by this browser.";}
  }
function showPosition(position)
  {
  x.innerHTML="Latitude: " + position.coords.latitude +
  "<br />Longitude: " + position.coords.longitude;
  }
</script>

Try it yourself »

HTML5 Canvas

The canvas element is used to draw graphics on a web page.

Your browser does not support the canvas element.

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What is Canvas?

The HTML5 canvas element uses JavaScript to draw graphics on a web page.
A canvas is a rectangular area, and you control every pixel of it.
The canvas element has several methods for drawing paths, boxes, circles, characters, and adding images.

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Create a Canvas Element

Add a canvas element to the HTML5 page.
Specify the id, width, and height of the element:

<canvas id="myCanvas" width="200" height="100"></canvas>

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Draw With JavaScript

The canvas element has no drawing abilities of its own. All drawing must be done inside a JavaScript:

<script type="text/javascript">
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
ctx.fillStyle="#FF0000";
ctx.fillRect(0,0,150,75);
</script>

Try it yourself »

JavaScript uses the id to find the canvas element:

var c=document.getElementById("myCanvas");

Then, create a context object:

var ctx=c.getContext("2d");

The getContext("2d") object is a built-in HTML5 object, with many methods to draw paths, boxes, circles, characters, images and more.
The next two lines draws a red rectangle:

ctx.fillStyle="#FF0000";
ctx.fillRect(0,0,150,75);

The fillStyle method makes it red, and the fillRect method specifies the shape, position, and size.

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Understanding Coordinates

The fillRect method above had the parameters (0,0,150,75).
This means: Draw a 150x75 rectangle on the canvas, starting at the top left corner (0,0).
The canvas' X and Y coordinates are used to position drawings on the canvas.
Mouse over the rectangle below to see the coordinates:

X

Y

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More Canvas Examples

Below are more examples of drawing on the canvas element:

Example - Line

Draw a line by specifying where to start, and where to stop:

Your browser does not support the canvas element.

Try it yourself »

Example - Circle

Draw a circle by specifying the size, color, and position:

Your browser does not support the canvas element.

Try it yourself »

Example - Gradient

Draw a gradient background with the colors you specify:

Your browser does not support the canvas element.

Try it yourself »

Example - Image

Put an image on the canvas:

Try it yourself »

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HTML5 <canvas> Tag

Tag	Description
<canvas>	Defines graphics

Complete Canvas 2d Reference

For a complete reference of all the attributes and methods that can be used with the canvas object, go to our complete canvas 2d reference.

HTML5 Audio

HTML5 provides a standard for playing audio files.

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Audio on the Web

Until now, there has not been a standard for playing audio files on a web page.
Today, most audio files are played through a plug-in (like flash). However, different browsers may have different plug-ins.
HTML5 defines a new element which specifies a standard way to embed an audio file on a web page: the <audio> element.

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How It Works

To play an audio file in HTML5, this is all you need:

Example

<audio controls="controls">
  <source src="song.ogg" type="audio/ogg" />
  <source src="song.mp3" type="audio/mpeg" />
  Your browser does not support the audio element.
</audio>

Try it yourself »

The control attribute adds audio controls, like play, pause, and volume.
You should also insert text content between the <audio> and </audio> tags for browsers that do not support the <audio> element.
The <audio> element allows multiple <source> elements. <source> elements can link to different audio files. The browser will use the first recognized format.

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Audio Formats and Browser Support

Currently, there are 3 supported file formats for the <audio> element: MP3, Wav, and Ogg:

Browser	MP3	Wav	Ogg
Internet Explorer 9	YES	NO	NO
Firefox 4.0	NO	YES	YES
Google Chrome 6	YES	YES	YES
Apple Safari 5	YES	YES	NO
Opera 10.6	NO	YES	YES

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HTML5 audio Tags

Tag	Description
<audio>	Defines sound content
<source>	Defines multiple media resources for media elements, such as <video> and <audio>

HTML5 Video + DOM

HTML5 <video> - Take Control Using the DOM

The HTML5 <video> element also has methods, properties, and events.
There are methods for playing, pausing, and loading, for example. There are properties (e.g. duration, volume, seeking) that you can read or set. There are also DOM events that can notify you, for example, when the <video> element begins to play, is paused, is ended, etc.
The examples below illustrate, in a simple way, how to address a <video> element, read and set properties, and call methods.

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HTML5 <video> - Methods, Properties, and Events

The table below lists the video methods, properties, and events supported by most browsers:

Methods	Properties	Events
play()	currentSrc	play
pause()	currentTime	pause
load()	videoWidth	progress
canPlayType	videoHeight	error
	duration	timeupdate
	ended	ended
	error	abort
	paused	empty
	muted	emptied
	seeking	waiting
	volume	loadedmetadata
	height
	width

Note: Of the video properties, only videoWidth and videoHeight are immediately available. The other properties are available after the video's meta data has loaded.

HTML5 Video

Videos on the Web

Until now, there has not been a standard for showing a video/movie on a web page.
Today, most videos are shown through a plug-in (like flash). However, different browsers may have different plug-ins.
HTML5 defines a new element which specifies a standard way to embed a video/movie on a web page: the <video> element.

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How It Works

To show a video in HTML5, this is all you need:

Example

<video width="320" height="240" controls="controls">
  <source src="movie.mp4" type="video/mp4" />
  <source src="movie.ogg" type="video/ogg" />
  Your browser does not support the video tag.
</video>

The control attribute adds video controls, like play, pause, and volume.
It is also a good idea to always include width and height attributes. If height and width are set, the space required for the video is reserved when the page is loaded. However, without these attributes, the browser does not know the size of the video, and cannot reserve the appropriate space to it. The effect will be that the page layout will change during loading (while the video loads).
You should also insert text content between the <video> and </video> tags for browsers that do not support the <video> element.
The <video> element allows multiple <source> elements. <source> elements can link to different video files. The browser will use the first recognized format.

---

Video Formats and Browser Support

Currently, there are 3 supported video formats for the <video> element: MP4, WebM, and Ogg:

Browser	MP4	WebM	Ogg
Internet Explorer 9	YES	NO	NO
Firefox 4.0	NO	YES	YES
Google Chrome 6	YES	YES	YES
Apple Safari 5	YES	NO	NO
Opera 10.6	NO	YES	YES

• MP4 = MPEG 4 files with H264 video codec and AAC audio codec
• WebM = WebM files with VP8 video codec and Vorbis audio codec
• Ogg = Ogg files with Theora video codec and Vorbis audio codec

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HTML5 video Tags

Tag	Description
<video>	Defines a video or movie
<source>	Defines multiple media resources for media elements, such as <video> and <audio>
<track>	Defines text tracks in mediaplayers

New Elements in HTML5

The internet has changed a lot since HTML 4.01 became a standard in 1999.
Today, some elements in HTML 4.01 are obsolete, never used, or not used the way they were intended to. These elements are deleted or re-written in HTML5.
To better handle today's internet use, HTML5 also includes new elements for better structure, drawing, media content, and better form handling.

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New Markup Elements

New elements for better structure:

Tag	Description
<article>	Specifies independent, self-contained content, could be a news-article, blog post, forum post, or other articles which can be distributed independently from the rest of the site.
<aside>	For content aside from the content it is placed in. The aside content should be related to the surrounding content
<bdi>	For text that should not be bound to the text-direction of its parent elements
<command>	A button, or a radiobutton, or a checkbox
<details>	For describing details about a document, or parts of a document
<summary>	A caption, or summary, inside the details element
<figure>	For grouping a section of stand-alone content, could be a video
<figcaption>	The caption of the figure section
<footer>	For a footer of a document or section, could include the name of the author, the date of the document, contact information, or copyright information
<header>	For an introduction of a document or section, could include navigation
<hgroup>	For a section of headings, using <h1> to <h6>, where the largest is the main heading of the section, and the others are sub-headings
<mark>	For text that should be highlighted
<meter>	For a measurement, used only if the maximum and minimum values are known
<nav>	For a section of navigation
<progress>	The state of a work in progress
<ruby>	For ruby annotation (Chinese notes or characters)
<rt>	For explanation of the ruby annotation
<rp>	What to show browsers that do not support the ruby element
<section>	For a section in a document. Such as chapters, headers, footers, or any other sections of the document
<time>	For defining a time or a date, or both
<wbr>	Word break. For defining a line-break opportunity.

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New Media Elements

HTML5 provides a new standard for media content:

Tag	Description
<audio>	For multimedia content, sounds, music or other audio streams
<video>	For video content, such as a movie clip or other video streams
<source>	For media resources for media elements, defined inside video or audio elements
<embed>	For embedded content, such as a plug-in
<track>	For text tracks used in mediaplayers

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The Canvas Element

The canvas element uses JavaScript to make drawings on a web page.

Tag	Description
<canvas>	For making graphics with a script

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New Form Elements

HTML5 offers more form elements, with more functionality:

Tag	Description
<datalist>	A list of options for input values
<keygen>	Generate keys to authenticate users
<output>	For different types of output, such as output written by a script

New Input Type Attribute Values

Also, the input element's type attribute has many new values, for better input control before sending it to the server:

Type	Description
tel	The input value is of type telephone number
search	The input field is a search field
url	The input value is a URL
email	The input value is one or more email addresses
datetime	The input value is a date and/or time
date	The input value is a date
month	The input value is a month
week	The input value is a week
time	The input value is of type time
datetime-local	The input value is a local date/time
number	The input value is a number
range	The input value is a number in a given range
color	The input value is a hexadecimal color, like #FF8800
placeholder	Specifies a short hint that describes the expected value of an input field

HTML5 Introduction

HTML5 is the next generation of HTML.

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What is HTML5?

HTML5 will be the new standard for HTML, XHTML, and the HTML DOM.
The previous version of HTML came in 1999. The web has changed a lot since then.
HTML5 is still a work in progress. However, most modern browsers have some HTML5 support.

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How Did HTML5 Get Started?

HTML5 is a cooperation between the World Wide Web Consortium (W3C) and the Web Hypertext Application Technology Working Group (WHATWG).
WHATWG was working with web forms and applications, and W3C was working with XHTML 2.0. In 2006, they decided to cooperate and create a new version of HTML.
Some rules for HTML5 were established:

• New features should be based on HTML, CSS, DOM, and JavaScript
• Reduce the need for external plugins (like Flash)
• Better error handling
• More markup to replace scripting
• HTML5 should be device independent
• The development process should be visible to the public

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New Features

Some of the most interesting new features in HTML5:

• The canvas element for drawing
• The video and audio elements for media playback
• Better support for local offline storage
• New content specific elements, like article, footer, header, nav, section
• New form controls, like calendar, date, time, email, url, search

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Browser Support

HTML5 is not yet an official standard, and no browsers have full HTML5 support.
But all major browsers (Safari, Chrome, Firefox, Opera, Internet Explorer) continue to add new HTML5 features to their latest versions.

Transaction Protocols

As a developer we no need to concern about transaction protocols and transaction manager used by WCF. WCF itself will take care of what kind of transaction protocols should be used for different situation. Basically there are three different kinds of transaction protocols used by WCF.

Transaction Propagation

In WCF, transaction can be propagated across service boundary. This enables service to participate in a client transaction and it includes multiple services in same transaction, Client itself will act as service or client.
We can specify whether or not client transaction is propagated to service by changing Binding and operational contract configuration

<bindings>
      <netTcpBinding>
        <binding transactionFlow="true"></binding>
      </netTcpBinding>
    </bindings>

Even after enabling transaction flow does not mean that the service wants to use the client’s transaction in every operation. We need to specify the “TransactionFlowAttribute” in operational contract to enable transaction flow.

[ServiceContract]
public interface IService
{

    [OperationContract]
    [TransactionFlow(TransactionFlowOption.Allowed)]
    int Add(int a, int b);

    [OperationContract]
    int Subtract(int a, int b);
}

Note: TransactionFlow can be enabled only at the operation level not at the service level.

TransactionFlowOption	Binding configuration
NotAllowed	transactionFlow="true" or transactionFlow="false"	Client cannot propagate its transaction to service even client has transaction
Allowed	transactionFlow="true"	Service will allow to flow client transaction. It is not necessary that service to use client transaction.
Allowed	transactionFlow="false"	If service disallows at binding level, client also should disable at binding level else error will be occurred.
Mandatory	transactionFlow="true"	Both Service and client must use transaction aware binding
Mandatory	transactionFlow="false"	InvalidOperationException will be throw when serice binding disables at binding level. FaultException will be thrown when client disable at its binding level.