Page 122 - DCAP202_Fundamentals of Web Programming

Unit 9: DOM Model

9.2.2 Event Object Notes

By using JavaScript, we have the ability to create dynamic web pages. Events are actions that can
be detected by JavaScript.
Every element on a web page has certain events which can trigger a JavaScript.

Example: We can use the onClick event of a button element to indicate that a function
will run when a user clicks on the button.
We define the events in the HTML tags.
Examples of events:

 A mouse click
 A web page or an image loading
 Mousing over a hot spot on the web page

 Selecting an input field in an HTML form
 Submitting an HTML form
 A keystroke

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

 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.

Did u know? 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!”.

 onFocus, onBlur and onChange: The onFocus, onBlur and onChange events are often used
in combination with validation of form fields.

Example: 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()”>
 onSubmit: The onSubmit event is used to validate ALL form fields before submitting it.

Example: 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.
<form method=”post” action=”xxx.htm” onsubmit=”return checkForm()”>

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