jQuery Event handlers - jQuery basic tutorial 8

8. jQuery Event handlers

We have the ability to create dynamic web pages by using events. Events are actions that can be detected by your Web Application.
Following are the examples events:

• A mouse click
• A web page loading
• Taking mouse over an element
• Submitting an HTML form
• A keystroke on your keyboard
• etc.

When these events are triggered you can then use a custom function to do pretty much whatever you want with the event. These custom functions call Event Handlers.

Binding event handlers:

Using the jQuery Event Model, we can establish event handlers on DOM elements with the bind() method as follows:

$('div').bind('click', function( event ){
   alert('Hi there!');
});
selector.bind( eventType[, eventData], handler)

Following is the description of the parameters:

• eventType: A string containing a JavaScript event type, such as click or submit. Refer to the next section for a complete list of event types.
  
• eventData: This is optional parameter is a map of data that will be passed to the event handler.
  
• handler: A function to execute each time the event is triggered.
  

Removing event handlers:

Typically, once an event handler is established, it remains in effect for the remainder of the life of the page. There may be a need when you would like to remove event handler.
jQuery provides the unbind() command to remove an exiting event handler. The syntax of unbind() is as follows:

selector.unbind(eventType, handler)

or 

selector.unbind(eventType)

Following is the description of the parameters:

• eventType: A string containing a JavaScript event type, such as click or submit. Refer to the next section for a complete list of event types.
  
• handler: If provided, identifies the specific listener that.s to be removed.
  

Event Types:

The following are cross platform and recommended event types which you can bind using JQuery:

Event Type	Description
blur	Occurs when the element loses focus
change	Occurs when the element changes
click	Occurs when a mouse click
dblclick	Occurs when a mouse double-click
error	Occurs when there is an error in loading or unloading etc.
focus	Occurs when the element gets focus
keydown	Occurs when key is pressed
keypress	Occurs when key is pressed and released
keyup	Occurs when key is released
load	Occurs when document is loaded
mousedown	Occurs when mouse button is pressed
mouseenter	Occurs when mouse enters in an element region
mouseleave	Occurs when mouse leaves an element region
mousemove	Occurs when mouse pointer moves
mouseout	Occurs when mouse pointer moves out of an element
mouseover	Occurs when mouse pointer moves over an element
mouseup	Occurs when mouse button is released
resize	Occurs when window is resized
scroll	Occurs when window is scrolled
select	Occurs when a text is selected
submit	Occurs when form is submitted
unload	Occurs when documents is unloaded

The Event Object:

The callback function takes a single parameter; when the handler is called the JavaScript event object will be passed through it.
The event object is often unneccessary and the parameter is omitted, as sufficient context is usually available when the handler is bound to know exactly what needs to be done when the handler is triggered, however there are certail attributes which you would need to be accessed.

The Event Attributes:

The following event properties/attributes are available and safe to access in a platform independent manner:

Property	Description
altKey	Set to true if the Alt key was pressed when the event was triggered, false if not. The Alt key is labeled Option on most Mac keyboards.
ctrlKey	Set to true if the Ctrl key was pressed when the event was triggered, false if not.
data	The value, if any, passed as the second parameter to the bind() command when the handler was established.
keyCode	For keyup and keydown events, this returns the key that was pressed.
metaKey	Set to true if the Meta key was pressed when the event was triggered, false if not. The Meta key is the Ctrl key on PCs and the Command key on Macs.
pageX	For mouse events, specifies the horizontal coordinate of the event relative from the page origin.
pageY	For mouse events, specifies the vertical coordinate of the event relative from the page origin.
relatedTarget	For some mouse events, identifies the element that the cursor left or entered when the event was triggered.
screenX	For mouse events, specifies the horizontal coordinate of the event relative from the screen origin.
screenY	For mouse events, specifies the vertical coordinate of the event relative from the screen origin.
shiftKey	Set to true if the Shift key was pressed when the event was triggered, false if not.
target	Identifies the element for which the event was triggered.
timeStamp	The timestamp (in milliseconds) when the event was created.
type	For all events, specifies the type of event that was triggered (for example, click).
which	For keyboard events, specifies the numeric code for the key that caused the event, and for mouse events, specifies which button was pressed (1 for left, 2 for middle, 3 for right)

The Event Methods:

There is a list of methods which can be called on an Event Object:

Method	Description
preventDefault()	Prevents the browser from executing the default action.
isDefaultPrevented()	Returns whether event.preventDefault() was ever called on this event object.
stopPropagation()	Stops the bubbling of an event to parent elements, preventing any parent handlers from being notified of the event.
isPropagationStopped()	Returns whether event.stopPropagation() was ever called on this event object.
stopImmediatePropagation()	Stops the rest of the handlers from being executed.
isImmediatePropagationStopped()	Returns whether event.stopImmediatePropagation() was ever called on this event object.

jQuery DOM manipulation - jQuery basic tutorial series 7

7. jQuery DOM manipulation 

JQuery provides methods to manipulate DOM in efficient way. You do not need to write big code to modify the value of any element's attribute or to extract HTML code from a paragraph or division.
JQuery provides methods such as .attr(), .html(), and .val() which act as getters, retrieving information from DOM elements for later use.

Content Manipulation:

The html( ) method gets the html contents (innerHTML) of the first matched element.
Here is the syntax for the method:

selector.html( )

Example:

Following is an example which makes use of .html() and .text(val) methods. Here .html() retrieves HTML content from the object and then .text( val ) method sets value of the object using passed parameter:

<html>
<head>
<title>the title</title>
   <script type="text/javascript" 
   src="/jquery/jquery-1.3.2.min.js"></script>
   <script type="text/javascript" language="javascript">
   
   $(document).ready(function() {

     $("div").click(function () {
      var content = $(this).html();
      $("#result").text( content );
    });

   });

   </script>
   <style>
      #division{ margin:10px;padding:12px;
                 border:2px solid #666;
                 width:60px;
               }
  </style>
</head>
<body>
   <p>Click on the square below:</p>
   <span id="result"> </span>
   <div id="division" style="background-color:blue;">
     This is Blue Square!!
   </div>
</body>
</html>

DOM Element Replacement:

You can replace a complete DOM element with the specified HTML or DOM elements. The replaceWith( content ) method serves this purpose very well.
Here is the syntax for the method:

selector.replaceWith( content )

Here content is what you want to have instead of original element. This could be HTML or simple text.

Example:

Following is an example which would replace division element with "<h1>JQuery is Great</h1>":

<html>
<head>
<title>the title</title>
   <script type="text/javascript" 
   src="/jquery/jquery-1.3.2.min.js"></script>
   <script type="text/javascript" language="javascript">
   
   $(document).ready(function() {

     $("div").click(function () {
       $(this).replaceWith("<h1>JQuery is Great</h1>");
    });

   });

   </script>
   <style>
      #division{ margin:10px;padding:12px;
                 border:2px solid #666;
                 width:60px;
               }
  </style>
</head>
<body>
   <p>Click on the square below:</p>
   <span id="result"> </span>
   <div id="division" style="background-color:blue;">
     This is Blue Square!!
   </div>
</body>
</html>

Removing DOM Elements:

There may be a situation when you would like to remove one or more DOM elements from the document. JQuery provides two methods to handle the situation.
The empty( ) method remove all child nodes from the set of matched elements where as the method remove( expr ) method removes all matched elements from the DOM.
Here is the syntax for the method:

selector.remove( [ expr ]) or selector.empty( )

You can pass optional paramter expr to filter the set of elements to be removed.

Example:

Following is an example where elements are being removed as soon as they are clicked:

<html>
<head>
<title>the title</title>
   <script type="text/javascript" 
   src="/jquery/jquery-1.3.2.min.js"></script>
   <script type="text/javascript" language="javascript">
   
   $(document).ready(function() {

     $("div").click(function () {
       $(this).remove( );
    });

   });

   </script>
   <style>
      .div{ margin:10px;padding:12px;
             border:2px solid #666;
             width:60px;
           }
  </style>
</head>
<body>
   <p>Click on any square below:</p>
   <span id="result"> </span>
   <div class="div" style="background-color:blue;"></div>
   <div class="div" style="background-color:green;"></div>
   <div class="div" style="background-color:red;"></div>
</body>
</html>

Inserting DOM elements:

There may be a situation when you would like to insert new one or more DOM elements in your existing document. JQuery provides various methods to insert elements at various locations.
The after( content ) method insert content after each of the matched elements where as the method before( content ) method inserts content before each of the matched elements.
Here is the syntax for the method:

selector.after( content ) or selector.before( content )

Here content is what you want to insert. This could be HTML or simple text.

Example:

Following is an example where <div> elements are being inserted just before the clicked element:

<html>
<head>
<title>the title</title>
   <script type="text/javascript" 
   src="/jquery/jquery-1.3.2.min.js"></script>
   <script type="text/javascript" language="javascript">
   
   $(document).ready(function() {

     $("div").click(function () {
       $(this).before('<div class="div"></div>' );
    });

   });

   </script>
   <style>
      .div{ margin:10px;padding:12px;
             border:2px solid #666;
             width:60px;
           }
  </style>
</head>
<body>
   <p>Click on any square below:</p>
   <span id="result"> </span>
   <div class="div" style="background-color:blue;"></div>
   <div class="div" style="background-color:green;"></div>
   <div class="div" style="background-color:red;"></div>
</body>
</html>

DOM Manipulation Methods:

Following table lists down all the methods which you can use to manipulate DOM elements:

Method	Description
after( content )	Insert content after each of the matched elements.
append( content )	Append content to the inside of every matched element.
appendTo( selector )	Append all of the matched elements to another, specified, set of elements.
before( content )	Insert content before each of the matched elements.
clone( bool )	Clone matched DOM Elements, and all their event handlers, and select the clones.
clone( )	Clone matched DOM Elements and select the clones.
empty( )	Remove all child nodes from the set of matched elements.
html( val )	Set the html contents of every matched element.
html( )	Get the html contents (innerHTML) of the first matched element.
insertAfter( selector )	Insert all of the matched elements after another, specified, set of elements.
insertBefore( selector )	Insert all of the matched elements before another, specified, set of elements.
prepend( content )	Prepend content to the inside of every matched element.
prependTo( selector )	Prepend all of the matched elements to another, specified, set of elements.
remove( expr )	Removes all matched elements from the DOM.
replaceAll( selector )	Replaces the elements matched by the specified selector with the matched elements.
replaceWith( content )	Replaces all matched elements with the specified HTML or DOM elements.
text( val )	Set the text contents of all matched elements.
text( )	Get the combined text contents of all matched elements.
wrap( elem )	Wrap each matched element with the specified element.
wrap( html )	Wrap each matched element with the specified HTML content.
wrapAll( elem )	Wrap all the elements in the matched set into a single wrapper element.
wrapAll( html )	Wrap all the elements in the matched set into a single wrapper element.
wrapInner( elem )	Wrap the inner child contents of each matched element (including text nodes) with a DOM element.
wrapInner( html	Wrap the inner child contents of each matched element (including text nodes) with an HTML structure.