Acting to an Event
The example below displays the date when a button is clicked:
Try it yourself »
<h1>My First Web Page</h1>
<button type="button" onclick="displayDate()">Display Date</button>
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
Note: 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.
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. For 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 John Doe!".
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()">
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()">
The onmouseover event can be used to trigger a function when the user mouse over an HTML element.
Try it yourself »