Tutorial 10 – Client-side development 1 - jQuery

1. Is jQuery a framework or a library? Discuss. 

jQuery: It's a library, not a framework

Is jQuery a JavaScript library?

jQuery is a fast, small, and feature-rich JavaScript library. It makes things like HTML document traversal and manipulation, event handling, animation, and Ajax much simpler with an easy-to-use API that works across a multitude of browsers.

2. Explain the features provided by jQuery? 

JQuery Features

1. Simple and easy: It have predefined method using you can perform any task easily compare to JavaScript. And it is easy to learn.
2. Lightweight: It is very lightweight library - about 19KB in size ( Minified and gzipped ).
3. CSS manipulation: It have predefined css() method for manipulate style for any Html elements.
4. Html manipulation: The jQuery made it easy to select DOM elements, traverse them and modifying their content.
5. Cross browser support: It support all modern web-browser including IE-6.
6. Event handling: It support event handling like click mouse button.
7. JavaScript Library: It is JavaScript library.
8. Ajax Support: It support ajax, you can develop a responsive and feature-rich site using AJAX technology.
9. Built-in Animation: It have predefined method "animate()" for create custom animation on web-page

3. Discuss the advantages and disadvantages of using jQuery in different project scales.

The advantages of jQuery

The main advantage of jQuery is that it is much easier than its competitors. You can add plugins easily, translating this into a substantial saving of time and effort. In fact, one of the main reasons why Resig and his team created jQuery was to buy time (in the web development world, time matters a lot).

The open source license of jQuery allows the library to always have constant and fast support, constantly publishing updates. The jQuery community is active and extremely hardworking.

Another advantage of jQuery over its competitors such as Flash and pure CSS is its excellent integration with AJAX.


The disadvantages of jQuery

One of the main disadvantages of jQuery is the large number of published versions in the short time. It does not matter if you are running the latest version of jQuery, you will have to host the library yourself (and update it constantly), or download the library from Google (attractive, but can bring incompatibility problems with the code).

In addition to the problem of the versions, other disadvantages that we can mention:

jQuery is easy to install and learn, initially. But it’s not that easy if we compare it with CSS
If jQuery is improperly implemented as a Framework, the development environment can get out of control.

4. Explain how the jQuery handles the issues related to partial page loads to the browser. 

Load ASP.NET MVC Partial Views Dynamically Using JQuery

Most of the times ASP.NET MVC views are rendered as a result of user navigating to some action. For example, when a user navigates to /home/index in the browser (either through address bar or through a hyperlink), ASP.NET MVC executes the action method and usually returns a view to the browser. This means each view is rendered as a result of a full GET or POST request. At times, however, you may want to load views dynamically through Ajax. This way you can render contents of a view without full page refresh.

5. Discuss the selectors and their use in jQuery. 

What is a jQuery selector?
A jQuery Selector is a function which makes use of expressions to find out matching elements from a DOM based on the given criteria. Simply you can say, selectors are used to select one or more HTML elements using jQuery. Once an element is selected then we can perform various operations on that selected element.

jQuery reads selectors from right to left.
Using an exact ID is fastest, followed by using an exact tag name, because they use optimized JavaScript-native methods.
Native CSS selectors like :first-child are faster than jQuery selectors like :first .

6. Compare and contrast the use of CSS advanced selectors in jQuery and jQuery’s DOM traversal API, indicating the pros and cons of them. 

CSS advanced selectors in jQuery
jQuery selectors allow you to select and manipulate HTML element(s). jQuery selectors are used to "find" (or select) HTML elements based on their name, id, classes, types, attributes, values of attributes and much more. It's based on the existing CSS Selectors, and in addition, it has some own custom selectors.


7. Explain the importance of DOM objects and DOM processing in jQuery. 

The functions associated with these objects determine how the objects may be manipulated, and they are part of the object model. The Document Object Model currently consists of two parts, DOM Core and DOM HTML. The DOM Core represents the functionality used for XML documents, and also serves as the basis for DOM HTML.

8. Discuss the benefits of using jQuery event handling over HTML event attributes, providing a list of events supported by jQuery.

jQuery Event Methods
Event methods trigger or attach a function to an event handler for the selected elements.
The following table lists all the jQuery methods used to handle events.

Commonly Used jQuery Event Methods
click() The click() method attaches an event handler function to an HTML element.
dblclick() The dblclick() method attaches an event handler function to an HTML element.

• mouseenter() 
• mouseleave() 
• mousedown() 
• mouseup() 

 9. Explain how to declare jQuery event handlers outside the $(document).ready() function, indicating the need for that, and the related issues and solutions for them. 

What is $( document .ready function () in jquery?

Definition and Usage. The ready event occurs when the DOM (document object model) has been loaded. Because this event occurs after the document is ready, it is a good place to have all other jQuery events and functions. Like in the example above. The ready() method specifies what happens when a ready event occurs.

10. Identify a list of advanced features provided by jQuery and explain their use towards improving the user experience

1) Use the Latest Version of jQuery

With all the innovation taking place in the jQuery project, one of the easiest ways to improve the performance of your web site is to simply use the latest version of jQuery. Every release of the library introduces optimizations and bug fixes, and most of the time upgrading involves only changing a script tag.

You can even include jQuery directly from Google's servers, which provide free CDN hosting for a number of JavaScript libraries.

<!-- Include a specific version of jQuery -->
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js"></script>

<!-- Include the latest version in the 1.6 branch -->
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6/jquery.min.js"></script>

The latter example will include the latest 1.6.x version automatically as it becomes available, but as pointed out on css-tricks, it is cached only for an hour, so you better not use it in production environments.

2) KEEP SELECTORS SIMPLE

Up until recently, retrieving DOM elements with jQuery was a finely choreographed combination of parsing selector strings, JavaScript loops and inbuilt APIs like getElementById(), getElementsByTagName() and getElementsByClassName(). But now, all major browsers support querySelectorAll(), which understands CSS query selectors and brings a significant performance gain.

However, you should still try to optimize the way you retrieve elements. Not to mention that a lot of users still use older browsers that force jQuery into traversing the DOM tree, which is slow.

$('li[data-selected="true"] a')   // Fancy, but slow
$('li.selected a')  // Better
$('#elem')  // Best

3) JQUERY OBJECTS AS ARRAYS

The result of running a selector is a jQuery object. However, the library makes it appear as if you are working with an array by defining index elements and a length.
// Selecting all the navigation buttons:
var buttons = $('#navigation a.button');

// We can loop though the collection:
for(var i=0;i<buttons.length;i++){
    console.log(buttons[i]);    // A DOM element, not a jQuery object
}

// We can even slice it:
var firstFour = buttons.slice(0,4);

If performance is what you are after, using a simple for (or a while) loop instead of $.each(), can make your code several times faster.

4) THE SELECTOR PROPERTY

jQuery provides a property which contains the selector that was used to start the chain.
$('#container li:first-child').selector    // #container li:first-child
$('#container li').filter(':first-child').selector    // #container li.filter(:first-child)

Although the examples above target the same element, the selectors are quite different. The second one is actually invalid - you can't use it as the basis of a new jQuery object. It only shows that the filter method was used to narrow down the collection.

5) CREATE AN EMPTY JQUERY OBJECT

Creating a new jQuery object can bring significant overhead. Sometimes, you might need to create an empty object, and fill it in with the add() method later.
var container = $([]);
container.add(another_element);

This is also the basis for the quickEach() method that you can use as a faster alternative to the default each().

6) SELECT A RANDOM ELEMENT

As I mentioned above, jQuery adds its own selection filters. As with everything else in the library, you can also create your own. To do this simply add a new function to the $.expr[':'] object. One awesome use case was presented by Waldek Mastykarz on his blog: creating a selector for retrieving a random element. You can see a slightly modified version of his code below:
(function($){
    var random = 0;

    $.expr[':'].random = function(a, i, m, r) {
        if (i == 0) {
            random = Math.floor(Math.random() * r.length);
        }
        return i == random;
    };

})(jQuery);

// This is how you use it:
$('li:random').addClass('glow');