JavaScript Events

JavaScript Events are items that transpire based on an action. A document event is the loading of an HTML document. A form event is the clicking on a button. Events are objects with properties.

Event Properties

x -Mouse x coordinate when the event happened.
y -Mouse y coordinate when the event happened.

JavaScript defines five types of events which are form, image, image map, link, and window events. Events are associated with HTML tags. The definitions of the events described below are as follows:

Form Events

blur - The input focus was lost.
change - An element lost the focus since it was changed.
focus - The input focus was obtained.
reset - The user reset the object, usually a form.
select - Some text is selected
submit - The user submitted an object, usually a form.

Image Events

abort - A user action caused an abort.
error - An error occurred.
load - The object was loaded.

Image Map Events

mouseOut - The mouse is moved from on top a link.
mouseOver - The mouse is moved over a link.

Link Events

click - An object was clicked.
mouseOut - The mouse is moved from on top a link.
mouseOver - The mouse is moved over a link.

Window Events

blur - The input focus was lost.
error - An error occurred.
focus - The input focus was obtained.
load - The object was loaded.
unload - The object was exited.

Event Association

Events are associated with HTML tags. The definitions of the events described below are as follows:

abort - A user action caused an abort of an image or document load.
blur - A frame set, document, or form object such as a text field loses the focus for input.
click - Happens when a link or image map is clicked on
change - Happens when a form field is changed by the user and it loses the focus.
error - An error happened loading a image or document.
focus - A frame set, document, or form object such as a text field gets the focus for input.
load - The event happens when an image or HTML page has completed the load process in the browser.
mouseOut - The event happens when the mouse is moved from on top of a link or image map
mouseOver - The event happens when the mouse is placed on a link or image map.
reset - The user reset the object which is usually a form.
submit - The user submitted an object which is usually a form.
unload - The object such as a framesed or HTML document was exited by the user.

The events for each HTML tag are as follows:

<A>
- click (onClick)
- mouseOver (onMouseOver)
- mouseOut (onMouseOut)
<AREA>
- mouseOver (onMouseOver)
- mouseOut (onMouseOut)
<BODY>
- blur (onBlur)
- error (onError)
- focus (onFocus)
- load (onLoad)
- unload (onUnload)
<FORM>
- submit (onSubmit)
- reset (onReset
<FRAME>
- blur (onBlur)
- focus (onFocus)
<FRAMESET>
- blur (onBlur)
- error (onError)
- focus (onFocus)
- load (onLoad)
- unload (onUnload)
<IMG>
- abort (onAbort)
- error (onError)
- load (onLoad)
<INPUT TYPE = "button">
- click (onClick)
<INPUT TYPE = "checkbox">
- click (onClick)
<INPUT TYPE = "reset">
- click (onClick)
<INPUT TYPE = "submit">
- click (onClick)
<INPUT TYPE = "text">
- blur (onBlur)
- focus (onFocus)
- change (onChange)
- select (onSelect)
<SELECT>
- blur (onBlur)
- focus (onFocus)
- change (onChange)
<TEXTAREA>
- blur (onBlur)
- focus (onFocus)
- change (onChange)
- select (onSelect)

Event Handlers

Event handlers are created as follows:

onEvent = "Code to handle the event"

The following example demonstrates its use:

As you can see, the event handling attribute is included in the HTML tag. When multiple statements are included in the event handling code, the statements are separated by a semicolon.
The following example can be used to redirect a link to another location:

<HTML>
<HEAD>
<TITLE>Using functions as event handlers</TITLE>
<SCRIPT LANGUAGE="JavaScript">
<!--
function nameDefined(ckie,nme)
{
   var splitValues
   var i
   for (i=0;i<ckie.length;++i)
   {
      splitValues=ckie[i].split("=")
      if (splitValues[0]==nme) return true
   }
   return false
}
function delBlanks(strng)
{
   var result=""
   var i
   var chrn
   for (i=0;i<strng.length;++i) {
      chrn=strng.charAt(i)
      if (chrn!=" ") result += chrn
   }
   return result
}
function getCookieValue(ckie,nme)
{
   var splitValues
   var i
   for(i=0;i<ckie.length;++i) {
      splitValues=ckie[i].split("=")
      if(splitValues[0]==nme) return splitValues[1]
   }
   return ""
}
function testCookie(cname, cvalue) {  //Tests to see if the cookie 
   var cookie=document.cookie        //with the name and value 
   var chkdCookie=delBlanks(cookie)  //are on the client computer
   var nvpair=chkdCookie.split(";")
   if(nameDefined(nvpair,cname))  //See if the name is in any pair
   {   
      tvalue=getCookieValue(nvpair,cname)  //Gets the value of the cookie
      if (tvalue == cvalue) return true
    else return false
   }
   else return false
}
function redirectLink() {
   if (testCookie("javahere", "yes")) {
      window.location="javahere.html"
   }
   else{
      var futdate = new Date()
      var expdate = futdate.getTime()
      expdate += 3600*1000  //expires in 1 hour(milliseconds)
      futdate.setTime(expdate)
      var newCookie="javahere=yes; path=/;"
      newCookie += " expires=" + futdate.toGMTString()
      window.document.cookie=newCookie
      window.location="javanot.html"
   }
}
//-->
</SCRIPT>
</HEAD>
<BODY>
<H3>Using an event handler to direct a link based on a cookie value</H3>
<P>
<A NAME="Here" onClick="return redirectLink()">See if you've been here.</A>
</P>
</BODY>
</HTML>

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Friday 23 March 2012