JavaScript
HTML DOM Events
HTML DOM
allows JavaScript to react to HTML events:
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Reacting to
Events
A JavaScript
can be executed when an event occurs, like when a user clicks on an HTML
element.
To execute
code when a user clicks on an element, add JavaScript code to an HTML event
attribute:
onclick=JavaScript
Examples of
HTML events:
When a user
clicks the mouse
When a web
page has loaded
When an
image has been loaded
When the
mouse moves over an element
When an
input field is changed
When an HTML
form is submitted
When a user
strokes a key
In this
example, the content of the <h1> element is changed when a user clicks on
it:
Example
<!DOCTYPE
html>
<html>
<body>
<h1
onclick="this.innerHTML = 'Ooops!'">Click on this text!</h1>
</body>
</html>
»
In this
example, a function is called from the event handler:
Example
<!DOCTYPE
html>
<html>
<body>
<h1
onclick="changeText(this)">Click on this text!</h1>
<script>
function
changeText(id) {
id.innerHTML = "Ooops!";
}
</script>
</body>
</html>
»
HTML Event
Attributes
To assign
events to HTML elements you can use event attributes.
Example
Assign an
onclick event to a button element:
<button
onclick="displayDate()">Try it</button>
»
In the
example above, a function named displayDate will be executed when the button is
clicked.
Assign
Events Using the HTML DOM
The HTML DOM
allows you to assign events to HTML elements using JavaScript:
Example
Assign an
onclick event to a button element:
<script>
document.getElementById("myBtn").onclick
= displayDate;
</script>
»
In the
example above, a function named displayDate is assigned to an HTML element with
the id="myBtn".
The function
will be executed when the button is clicked.
The onload
and onunload Events
The onload
and onunload events are triggered when the user enters or leaves the page.
The onload
event can be used to check the visitor's browser type and browser version, and
load the proper version of the web page based on the information.
The onload
and onunload events can be used to deal with cookies.
Example
<body
onload="checkCookies()">
»
The onchange
Event
The onchange
event is often used in combination with validation of input fields.
Below is an
example of how to use the onchange. The upperCase() function will be called
when a user changes the content of an input field.
Example
<input
type="text" id="fname" onchange="upperCase()">
»
The
onmouseover and onmouseout Events
The
onmouseover and onmouseout events can be used to trigger a function when the
user mouses over, or out of, an HTML element:
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Me
»
The
onmousedown, onmouseup and onclick Events
The
onmousedown, onmouseup, and onclick events are all parts of a mouse-click.
First when a mouse-button is clicked, the onmousedown event is triggered, then,
when the mouse-button is released, the onmouseup event is triggered, finally,
when the mouse-click is completed, the onclick event is triggered.
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»
More
Examples
onmousedown
and onmouseup
Change an
image when a user holds down the mouse button.
onload
Display an
alert box when the page has finished loading.
onfocus
Change the
background-color of an input field when it gets focus.
Mouse Events
Change the
color of an element when the cursor moves over it.
HTML DOM
Event Object Reference
For a list
of all HTML DOM events, look at our complete HTML DOM Event Object Reference.
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