# Thursday, January 30, 2014
# Wednesday, January 29, 2014

Ajax refers to the pattern of calling server-side methods from client-side JavaScript. jQuery provides a simple, straightforward method for making Ajax calls. The syntax is

$.ajax({
            url: ServiceEndpoint,
            dataType: ReturnDataType,
            type: HttpVerb,
            data: Data,
            error: function (err) {
                // Code to run when error returned
            },
            success: function (data) {
                // Code to run when successfully returned
            }
          });

where

  • ServiceEndpoint is the URL of the method to call on the server
  • ReturnDataType is the data format we expect the server method to return (“xml”, “html”, “script”, “json”, “jsonp”, or “text”). You can specify multiple values and the server will return the first matching format type that is supported by this method.
  • HttpVerb is the HTTP verb (“GET”, “POST”, “PUT”, or “DELETE”) to use to send data to the server.
  • Data is the data (if any) that is sent from the client to the server.

By default the Ajax method executes asynchronously. When a call returns from the server, jQuery will run the function specified in the success parameter (if the call returned successfully); or the function in the error parameter if an exception occurred. These functions accept return data or error information returned from the server as parameters, so that your client-side code can handle return values effectively.

Ajax can provide a much more responsive experience to your web page and jQuery can make ease the process of making Ajax calls.

Wednesday, January 29, 2014 5:03:00 PM (GMT Standard Time, UTC+00:00)
# Sunday, January 26, 2014

In the last article, I showed how to use jQuery to select elements in the Document Object Model (DOM) of a web page. In this article, I will show things you can do with those selections.

Calling Methods on Selections

We can call methods on the list of objects returned by a selection simply by appending a dot, followed by the method call and any arguments to the selection syntax. For example, the following jQuery will hide all the anchor tags on a page:

$(“a”).hide();

Binding Functions to Selections

One of the powers of jQuery is the ease with which we can bind a function to the events of an object, so that this function executes whenever the event fires. To do so, simply append a selection with a dot followed by the name of the event; then, pass the function as an argument to the event, as shown below:

$(selection).eventname(function(){
…
}

For example, the click event fires when a user clicks on a page element. The following sample binds a function to the click event of an element with the ID “Div1”:

$(“#Div1”).click(function(){
…
}

The (document).ready event

The document variable is defined within the jQuery script. Selecting this variable with $(document) will return the document as a whole. The most common use for this selector is to bind a function to the document’s ready event. The syntax for this is

$(document).ready(function(){
    …
});

I have omitted the body of the function in this case, but notice the anonymous function declaration. In JavaScript, we don’t need to assign a name to a function if we are binding it to an event – we only need to pass that function to the method name. This is common syntax in JavaScript.

In fact, binding a function to the document ready event is so common, that its syntax can be shortened to simply surrounding a function with parentheses preceded by “$”, as shown in the following snippet, which does the same thing as the previous snippet

$(function(){
    …
});

Putting it All Together

We can nest functions in jQuery and we often do so by binding code to events when the document.ready event fires, as in the following example:
<script type="text/javascript" src="jquery-1.10.2.min.js"></script>
<script type="text/javascript">
   $(function(){
    $(“#HideTextDiv”).click(function(){
     $(“#Div1”).hide();
    });
    $(“#ShowTextDiv”).click(function(){
     $(“#Div1”).show();
    });
   });
</script>

In this article, I showed how to manipulate selected elements and bind events to those elements. This can be done when a page loads by adding code to the document.ready event.

Sunday, January 26, 2014 5:00:00 PM (GMT Standard Time, UTC+00:00)
# Saturday, January 25, 2014

How JavaScript Interacts with a Web Page

When a web page loads in a web browser, the browser loads all elements into memory. Each element on a page exists in a containership hierarchy – that is, each element is contained within another element with the document itself at the top of this containership hierarchy. Containership is defined by tags that are opened and closed between the opening and closing tags of another element. For example, the simple page in the listing below is loaded into memory in an object graph similar to that shown in Figure 1.

<html>
  <head>
    <title>My Page</title>
    <script
       type="text/javascript“
       src="http://code.jquery.com/jquery-1.7.1.min.js ">
    </script>
  </head>
  <body>
    <div>
       <p>
          This a <a href="Page2.htm">link</a>
       </p>
    </div>
    <div>
       Colors:
       <ul>
          <li>Red</li>
          <li>Orange</li>
          <li>Yellow</li>
       </ul>
    </div>
  </body>
</html>

image 
Fig. 1

jQuery keyword

Because jQuery is JavaScript, it can be mixed with native JavaScript in your script files. The jQuery object is defined in the jQuery file and you can use it via the “jQuery” keyword. This keyword tells the parser that what follows is jQuery syntax. This keyword is so common that it can be shortened to the simpler “$”.

“$” is used to define selectors and to call methods defined in the jQuery scripts.

Selectors

Most of what you will do with jQuery involves selecting a set of objects and performing some action on those objects, such as

· Changing the properties of each object in the set

· Binding code to an event of the objects

· Calling a method on each object

You can return a set of objects with the following jQuery syntax:

$(selector)

where selector is a snippet identifying which objects to select. The syntax of a jQuery selector is similar to the syntax for a CSS selector. The most common selectors are for a tag, and ID, and a Class Name, as shown in the list below.

Selector

Select by…

Example

“#xxx”

ID

$(“#MyDiv”)

“.xxx”

Class Name

$(“.MyClass”)

“xxx”

Element Type

$(“a”)

Xxx

Variable Name

$(document)

A selector preceded by “#” will be interpreted as an ID selector. jQuery will search the page for any element that matches the ID that follows “#” in the selector.

A selector preceded by “.” will be interpreted as a Class selector. jQuery will search the page for any element assigned the name of the Class that follows “.” in the selector.

A selector with no preceding characters will be interpreted as a Tag selector. jQuery will search the page for any element with the tag name identified in the selector.

Advanced Selectors

Combining Selectors

It is possible to combine selectors to either narrow your selection or establish containership.

Two selectors separated by a space indicate that jQuery should select the second selector only if it is found within the first selector. For example, $(“div a”) selects every anchor tag that is contained within a div tag.

Two selectors concatenated without a space indicate that jQuery should select only objects that match both selection criteria. For example, $(“div.BodyText”) selects any div tag that contains the attribute class=”BodyText”.

Set-based Selectors

By default, jQuery selectors always select a set of elements, even if that set may contain zero, one, or more than one element. However, we can refine a selection further by appending filters to a selection, such as “:first”, to select only the first element in the selected list of elements; “:last”, to select the last element in the selected list; “:even”, to select only the even-numbered elements; and “:odd”, to select only the odd-numbered elements. When even and odd selectors, it is important to note that the sets start with index number 1.

For example, $(“div:first”) selects the first div on the page, while $(“a:even”) selects every other anchor on the page, beginning with the second.

In this article, I described how to select objects on a web page with jQuery. In the next article, I will show things that we can do with those selections.

Saturday, January 25, 2014 5:56:00 PM (GMT Standard Time, UTC+00:00)
# Friday, January 24, 2014

Accessing jQuery From Your Site

To start using jQuery, simply add a reference to the jQuery library as in the following example:

<script 
    type="text/javascript" 
    src="scripts/jquery-1.10.2.min.js"></script>

Of course, you will need to download jQuery from http://jQuery.com and save it in your site’s scripts folder for the location above to work. Also, the currently downloaded version may have a slightly different name as the version number is included in the file name.

Using a Content Delivery Network

Alternatively, you can connect to jQuery on a Content Delivery Network (CDN), such as one provided by jQuery, Microsoft, or Google, in the following manner:

<script 
  type="text/javascript" 
  src=“http://ajax.microsoft.com/ajax/jquery/jquery-1.10.2.min.js">
</script>

or

<script 
  type="text/javascript"
  src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js">
</script>

or

<script 
  type="text/javascript" 
  src="http://code.jquery.com/jquery-1.10.2.min.js ">
</script>

A CDN offers the following advantages:

  1. A CDN has servers around the world, so it can serve up files closer to the client that requested them, so they download faster.
  2. Most web clients cache files by default, so the client may already have a cached copy of the jQuery script file and may not need to download it again.

Adding jQuery to your site or page is simple and fast. In my next article, I will talk about the syntax of jQuery and how to use it to select objects on a web page.

Friday, January 24, 2014 5:42:00 PM (GMT Standard Time, UTC+00:00)
# Thursday, January 23, 2014

I began to write web applications in the 1990s and, from the beginning, I understood that client-side scripting would enhance my applications. If I wanted to update part of a web page, client-side scripting could do so quickly and elegantly and without sending a new request to the server or refreshing the entire page and I knew it.

JavaScript quickly became the de facto language of the web and, unfortunately, I was never very good at JavaScript. One reason I struggled with JavaScript was because each browsers implemented JavaScript in its own way and sometimes the language diverged from one browser to the next. For example, the following JavaScript code is necessary to perform the simple task of retrieving an element from a web page:

var id = "Div1";
var elm = null;
  if (document.getElementById)
  {
    elm = document.getElementById(id);
  }
  else if (document.all)
  {
    elm = document.all[id];
  }
  else if (document.layers)
  {
    elm = document.layers[id];
  }

Notice there are several different JavaScript commands that retrieve an element by its ID. Some commands work in some browsers, but not in others. The code snippet above has to test the validity of each command until it settles on one that works within the current browser.

This simple task is complicated by the different JavaScript engines.

Eventually, I discovered jQuery and the problem of cross-browser client-side program went away. jQuery is a JavaScript library that allows a developer to write code that works across disparate browsers, without the necessity of trying multiple commands. The jQuery core library takes care of the different JavaScript implementations. For example, the code above is simplified in jQuery to

var elm = $("#Div1");

This is a simple task, yet it underscores the terseness and simplicity of jQuery. All the cross-platform code is abstracted away when I use jQuery, making my JavaScript much easier to read and maintain.

Thursday, January 23, 2014 5:37:00 PM (GMT Standard Time, UTC+00:00)
# Thursday, January 24, 2013

Here are the slides and demos from my How I Learned to Stop Worrying and Love jQuery presentation at the 2013 CodeMash conference.

Demos and Slides

Thursday, January 24, 2013 2:07:42 AM (GMT Standard Time, UTC+00:00)
# Monday, October 3, 2011
Monday, October 3, 2011 5:06:48 AM (GMT Daylight Time, UTC+01:00)
# Wednesday, August 4, 2010
Wednesday, August 4, 2010 1:10:28 PM (GMT Daylight Time, UTC+01:00)
# Friday, July 9, 2010

BooksOfDavid

You might think that full-color illustrations would make very little difference in a technical book.

But  Beginning JavaScript and CSS Development with jQuery by Richard York focuses so much on user interfaces that the added color makes the samples more clear. When the author lists code to change the color of a paragraph, the illustration shows the new and old colors to drive home the concept.

York starts with the basics of jQuery – selecting elements on a page and applying styles dynamically – and moves progressively into more advanced topics, such as making Ajax calls and accessing the jQuery API. He devotes about a third of the book to jQueryUI, a library that contains controls designed to build rich, interactive web interfaces without the need for a lot of code.

York explains the challenges inherent in developing applications with Javascript (the need code to different Document Object Models for each browser) and how jQuery addresses this by providing a single programming model that abstracts away the different browser DOMS.

The book is filled with examples, showing the HTML, CSS and jQuery demonstrating each point. You can read/copy these from the book or download them from the Wrox site.

This book is aimed at someone with experience in HTML and CSS, but little to no Javascript or jQuery knowledge. For those just getting started in jQuery this is an easy to follow book where you can learn the concepts and quickly become productive.

Friday, July 9, 2010 5:28:10 PM (GMT Daylight Time, UTC+01:00)
# Monday, May 10, 2010

Episode 86

In this episode, David Hoerster describes how he uses jQuery and WCF to create rich, interactive applications.

Monday, May 10, 2010 11:18:51 AM (GMT Daylight Time, UTC+01:00)
# Monday, May 3, 2010

Episode 84

In this interview, John Petersen describes how to use jQuery, JSON and Ajax to enhance an ASP.Net MVC application.

Monday, May 3, 2010 11:28:46 AM (GMT Daylight Time, UTC+01:00)