HTML events are “things” that happen to HTML elements.
When JavaScript is used in HTML pages, JavaScript can “react” on these events.
HTML Events
An HTML event can be something the browser does, or something a user does.
Here are some examples of HTML events:
- An HTML web page has finished loading
- An HTML input field was changed
- An HTML button was clicked
Often, when events happen, you may want to do something.
JavaScript lets you execute code when events are detected.
HTML allows event handler attributes, with JavaScript code, to be added to HTML elements.
With single quotes:<elementevent=‘some JavaScript‘>
With double quotes:<elementevent=“some JavaScript“>
In the following example, an onclick attribute (with code), is added to a <button> element:
Example
<!DOCTYPE html>
<html>
<body>
<button onclick="document.getElementById('demo').innerHTML=Date()">The time is?</button>
<p id="demo"></p>
</body>
</html>
Result:
Result Shown in your browser.
In the example above, the JavaScript code changes the content of the element with id=”demo”.
In the next example, the code changes the content of its own element (using this.innerHTML):
Example
<!DOCTYPE html> <html> <body> <h2>JavaScript HTML Events</h2> <button onclick="this.innerHTML=Date()">The time is?</button> </body> </html>
Result:
Result Shown in your browser.
JavaScript code is often several lines long. It is more common to see event attributes calling functions:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript HTML Events</h2>
<p>Click the button to display the date.</p>
<button onclick="displayDate()">The time is?</button>
<script>
function displayDate() {
document.getElementById("demo").innerHTML = Date();
}
</script>
<p id="demo"></p>
</body>
</html>
Result:
Result Shown in your browser.
Common HTML Events
Here is a list of some common HTML events:
| Event | Description |
|---|---|
| onchange | An HTML element has been changed |
| onclick | The user clicks an HTML element |
| onmouseover | The user moves the mouse over an HTML element |
| onmouseout | The user moves the mouse away from an HTML element |
| onkeydown | The user pushes a keyboard key |
| onload | The browser has finished loading the page |
JavaScript Event Handlers
Event handlers can be used to handle and verify user input, user actions, and browser actions:
- Things that should be done every time a page loads
- Things that should be done when the page is closed
- Action that should be performed when a user clicks a button
- Content that should be verified when a user inputs data
- And more …
Many different methods can be used to let JavaScript work with events:
- HTML event attributes can execute JavaScript code directly
- HTML event attributes can call JavaScript functions
- You can assign your own event handler functions to HTML elements
- You can prevent events from being sent or being handled