Page 142 - DCAP202_Fundamentals of Web Programming

Unit 11: Handling Events Using JavaScript

11.1 Working on Event Notes

Events are normally used in combination with functions, and the function will not be executed
before the event occurs!

11.1.1 onLoad and onUnload

The onLoad and onUnload events are triggered when the user enters or leaves the page.
The onLoad event is often used to check the visitor’s browser type and browser version, and
load the proper version of the web page based on the information.
Both the onLoad and onUnload events are also often used to deal with cookies that should be set
when a user enters or leaves a page.

Example: You could have a popup asking for the user’s name upon his first arrival to
your page. The name is then stored in a cookie. Next time the visitor arrives at your page, you
could have another popup saying something like: “Welcome upendra!”.

11.1.2 onFocus, onBlur and onChange

The onFocus, onBlur and onChange events are often used in combination with validation of
form fields.
Below is an example of how to use the onChange event. The checkEmail() function will be called
whenever the user changes the content of the field:
<input type=”text” size=”30" id=”email” onchange=”checkEmail()”>

11.1.3 onSubmit

The onSubmit event is used to validate ALL form fields before submitting it.
Below is an example of how to use the onSubmit event. The checkForm() function will be called
when the user clicks the submit button in the form. If the field values are not accepted, the
submit should be cancelled. The function checkForm() returns either true or false. If it returns
true the form will be submitted, otherwise the submit will be cancelled:
<form method=”post” action=”xxx.htm” onsubmit=”return checkForm()”>

11.1.4 onMouseOver and onMouseOut

onMouseOver and onMouseOut are often used to create “animated” buttons.
Below is an example of an onMouseOver event. An alert box appears when an onMouseOver
event is detected:
<a href=”a.html” onmouseover=”alert(‘An onMouseOver event’);return false
</a>
Self Assessment

Fill in the blanks:
1. .............................. are normally used in combination with functions, and the function will
not be executed before the event occurs!
2. The .............................. and onUnload events are triggered when the user enters or leaves
the page.

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