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.